The Hand of Irulegi was found in 2021, so there is not much scholarship on it yet. I will try to answer your questions based on what I know about Basque linguistics, keeping in mind that some things might turn out to be incorrect, as more and more ancient Basque texts come to light.
(a) Is the inscription genuine?
If by genuine you mean "written in ancient times", then, as far as I know, the paleographers and linguists who have examined it agree that the object and the inscription carved on it are both ancient. Even Javier Velaza and Joaquín Gorrochategui, who are notoriously cautious when it comes to the discussion of Basque antiquities (and rightly so, I would add), think the Hand of Irulegi has good chance of being authentic (cf. this conference for their opinions on this matter). There are no hints that the text is a forgery: the techniques used to write it are consistent with the antiquity of the artifact, and the hand-shaped bronze plate used as an amulet is frequent in the Iberian and Celtiberian imagery and art.
(b) Is the transcription reliable and secure?
I would say that, leaving aside the obscure T-shaped sign in the third line, we can safely conclude the text was written using a variant of the Iberian script. But I would like to add a few details.
First, the text has actually been inscribed twice: initially, somebody carved the letters on the bronze plate, and then he (or maybe someone else) proceeded to punctuate each letter guided by the signs previously carved on the artifact. Thanks to the work of the second scribe, we can isolate each word in the text with reasonable certainty, since he also added dots serving as word separators.
Second, the script in which the text of the artifact is written is a non-dual form of the Northeastern variant of the Iberian signary augmented with the aforementioned T-shaped sign. This is crucial to the reading and interpretation of the text. One may think we are dealing with a Celtiberian inscription, as the Celtiberian script is very similar to the Northeastern Iberian script (in fact the former derived from the latter), but this is not the case because the Celtiberian signary only has one kind of ⟨r⟩ sign, while the Iberian signary, has two rhotic elements, transliterated as ⟨r⟩ and ⟨ŕ⟩. Given that the text of the artifact exhibits these two /r/ as well, we infer it has been written using a variant of the Iberian script. Velaza (see previous link) is even convinced the text of the Hand of Irulegi should be understood as an example of what he calls the Vasconic signary, a special variant of the Northeastern Iberian script which may have been employed (to a very limited extent) by the ancient Basque people. As a matter of fact, the peculiar ⟨T⟩ sign is not new, it has been found before on coins dug up throughout the Basque territory. So, in some sense we see continuity between this artifact and what we know from independent archeological findings.
(c) Does this short text really justify the assumption that the language is Ancient Basque?
From what I have read and seen, I think there is convincing evidence that the inscription, or at least part of it, represents the oldest recognizable text written in the Basque language. I will leave the discussion of the word ⟨sorioneku⟩ for part (d), for the moment we should bear in mind that just because the text was written in Iberian script it does not necessarily mean that the underlying language was Iberian. In addition to this, it is reasonable to assume the Basque interpretation of the first word is the correct one because, as I have said, such hand-shaped amulets were commonly put on gates and doors of ancient houses to wish good fortune and prosperity to the dwellers. The scribe of the Hand of Irulegi even drew the three major hand lines of the palm, which in the Ancient World were associated with one's luck or misfortune.
(d) Is the shape of the first word in accordance with scholarly reconstructions of Proto-Basque?
Yes, the shape of the first word agrees remarkably well with reconstruction of Proto-Basque. To this day, there are two major reconstructions of Proto-Basque: the first one, which probably coincides with the language of the Hand of Irulegi, was proposed by Luis Michelena (1961). This represents a rather late stage of the Proto-Basque language, spoken just before the various dialects began to diverge. More recently, Joseba Lakarra (cf. 1995, 1996, 2002, 2006, 2009, 2019 inter alia) reconstructed an older stage of Proto-Basque (we might even call it Pre-Proto-Basque) employing the methodology of internal reconstruction. These two are by far the most conservative and cautious reconstructions of the language I know of. I am not considering Blevins' (2018) attempt at reconstructing Proto-Basque here, since it is highly controversial and widely criticized, if not completely rejected, by professional Bascologists.
By the beginning of the Middle Ages, Basque dialects had already begun diverging, so it makes sense to compare the text of the Hand of Irulegi (which dates back to 80-70 c. BCE) with Michelena's reconstruction of Proto-Basque. But what can we say about the shape of the text?
Of course, starting from the first line, we encounter the emblematic ⟨sorioneku⟩. First of all, if the equation with Modern Basque zorioneko is correct, it does not mean "good fortune", but "lucky, fortuned", lit. "(one) of good luck". The word is analyzed as zori "fortune" + on "good", giving rise to zorion "good fortune", to which the relational suffix -(e)ko is added. This suffix is very productive and has many functions, but here it is used to derive an adjective from a headless noun phrase. In Michelena's reconstruction the first component of this word could come from Proto-Basque *zori or *zoli, because in his system *r and *l merged into r between vowels. Although he did not reconstruct this word explicitly in Proto-Basque, Michelena contrasted it with zori, zorhi (N, LN, L, Z), zoli (B) "ripe, mature", which he thought had an original *l, as the archaic Biscayan variant and its verbal derivate zoldu seem to show (Michelena 1961: 180 fn. 2, 319-20, 208). By this logic, we could probably guess that the proto-form of zori "fortune" was indeed *zori to avoid homophony with zor(h)i "ripe". Moreover, the text of the Hand of Irulegi spells this word with ⟨r⟩, and not with ⟨l⟩ (both signs were present in the Iberian script), thus pointing to an original rhotic segment, instead of a liquid.
The word zori "fortune" is akin to txori (B, G, N, LN, R), xori (N, L, LN) "bird", reminiscent of Latin auspex "augur" < PIt. *avi-spek-s "observer of birds" (Trask 2008: 377-78). So, the older meaning of zori should have been something like "omen".
The inscription on the Hand of Irulegi is also remarkable in another sense: it offers an attestation for the word zori (and for its derivative zorion) previous to 1545.
Following Gorrochategui's suggestions (see link above), we might even go further. He speculates that ⟨tenekebeekiŕateŕe[n]⟩ in line 2 could be separated as ⟨tenekebe ekiŕateŕe[n]⟩, because a sequence of two identical vowels is not allowed in the same word. As for ⟨oTiŕtan⟩ (line 3), this may be a noun in the inessive case (cf. Basque -an). The sequence ⟨eseakaŕi⟩ (line 3) may be a compound where the first element ⟨ese⟩ could stand for Basque etxe "house". Lastly, if this text is a complete sentence, we should expect to find a finite verb, and this may be identified with ⟨eŕaukon⟩ (line 4), according to Gorrochategui. Obviously, these are all mere conjectures, but they seem to fit quite nicely with the Basque interpretation of the first line.
There are a few difficulties with the Basque interpretation of the Hand of Irulegi, such as the exact reading of the sign ⟨ku⟩, which is oddly written as ⟨ke⟩ by the first scribe (was it a mistake corrected by the second scribe, or was it on purpose?), and the ambiguity in the writing of sibilants (Basque has six: z, s, x, tz, ts and tx, but only ⟨s⟩ is present in the text) and rhotics (Basque has a contrast between fortis rr vs. lenis r, but it is not clear how this is reflected in the language of the inscription, where both ⟨r⟩ and ⟨ŕ⟩ are present). Despite these issues, I still think the Basque interpretation is viable. Some inconsistencies with our knowledge of Modern Basque are to be expected, given that we are supposedly dealing with an ancient stage of the language never documented until now.
B = Biscayan; G = Guipuzkoan; L = Lapurdian; LN = Lower Navarrese; N = (Upper) Navarrese; R = Roncalese; Z = Souletin.
- Blevins, Juliette 2018. Advances in Proto-Basque reconstruction with evidence for the Proto-Indo-European-Euskarian hypothesis. London & New York: Routledge.
- Iberian script, on Wikipedia.
- La mano de Irulegi | Aranzadiren Arkeologia Jardunaldiak (in Spanish), conference uploaded on the YouTube channel San Telmo Museoa.
- Lakarra, Joseba A. 1995. "Reconstructing the Pre-proto-Basque root". In Hualde J. I., Lakarra J. A. and Trask R. L. (eds.) Towards a History of the Basque Language. Amsterdam: John Benjamins, pp. 189-206.
- Lakarra, Joseba A. 1996. "Sobre el europeo antiguo y la reconstrucción del protovasco". Anuario del Seminario de Filología Vasca «Julio de Urquijo» 30: 1-70.
- Lakarra, Joseba A. 2002. "Etymologiae (proto)uasconicae LXV". In Artiagoitia X. et al. (eds.) Erramu Boneta. Festschrift for Rudolf P. G. de Rijk. San Sebastián: UPV/EHU, pp. 425-442.
- Lakarra, Joseba A. 2006. "Protovasco, munda y otros: reconstrucción interna y tipología holística diacrónica". Oihenart 21: 229-322.
- Lakarra, Joseba A. 2009. "Forma Canónica y cambios en la Forma Canónica en la prehistoria de la lengua vasca". Palaeohispanica 9: 557-609.
- Lakarra, Joseba A., Manterola, Julen and Segurola, Iñaki 2019. Euskal Hiztegi Historiko-Etimologikoa [Basque Historical-Etymological Dictionary]. Euskaltzaindia.
- Michelena, Luis 1961. Fonética Histórica Vasca. San Sebastián: Publicaciones del Seminario «Julio de Urquijo».
- Trask, Larry R., Wheeler, Max W. (ed.) 2008. Etymological Dictionary of Basque. University of Sussex.