The first year of the improved synchro, which I think you are asking, was 1939. All gearsets from then through 1948 had the same synchro except for a minor change in 1940.
While preferring the V8s; had eight or ten, I did have a couple of Model As, a `28 and `31. I don`t recall having to double de-clutch between 1st-2nd and 2nd-3rd. Didn`t they have a form of synchromesh or were my transmissions just so shot it didn`t matter? (It was a long time ago. Maybe my brain is as worn as the gearboxes were.....)