This is just one example: In the word "father", there is the interdental voiced fricative. However, in Old English, the word is fæder with a voiced alveolar stop; it is also fader in Middle English. The German word is Vater which has the voiceless stop from the voiced stop, which makes sense if the original sound was a voiced stop, but the Gothic word fadar and the Old Norse word faðir both contain fricatives. And I've never read anything about the High German Consonant Shift affecting anything twice. There are also other words like that, such as the word "word". So is the voiced stop the original sound or was there some amount of th-stopping in Proto-West Germanic?