Hasselblad back question

Question: Some Hasselblad backs I see advertised as "A12 back with 12 release". What does the "12 release" mean?

Thanks,

Mark

Later A12 backs have "12" printed on the release button. Earlier A12 backs have a "V" in a circle on the release button. I'm not sure at what point the older "flip-up" spool retainers on the film magazine were changed to the "toggle" spool retainers, but this may coincide with the release button change. The "V" backs are older.

Peter Gomena