I am aware of the fact that this question is rather specific, but anyway I would like to give it a try.
Japanese Sign Language has three manual alphabets: one for representing kana-characters, and two for Latin characters. The first Latin-character manual alphabet is adopted from American Sign Language (ASL) with minor adjustments. My question concerns the second Latin-character manual alphabet which I call "JSL Latin manual alphabet". All three can be viewed here: http://www2s.biglobe.ne.jp/~kem/yubimoji/yubi-gaz.htm
They are used according to the purpose. According to my personal experience, when spelling a string of Latin letters such as the name of an internet page or the title of a movie, most commonly signers would use the ASL-based manual alphabet. On the other hand, when the letters form an abbreviation such as "NHK" or when a single character is combined with numerals such as in "B8" (designating a subway exit number), signers would tend to use the JSL Latin manual alphabet. I also noted an age difference: Younger JSL signers are more apt to use the ASL-based manual alphabet while the older generation prefers the JSL Latin manual alphabet. Still, both are presently in use.
My question concerns the JSL Latin manual alphabet (i.e. the last one on the page above). It is perculiar as it at times uses one hand, at other times both hands. I have checked a list of manual alphabets of the world (http://www.michaelszczepanski.de/fingerabc.html), but it does not resemble any other manual alphabet that I have seen so far.
When and where was it introduced into the Japanese Sign Language and what is it based on?