If I read my Browning book correctly, the A5 in 20ga wasn't introduced til mid 1958.
No pre-war A-5's were made in 20ga,,only 12 and 16.

Betw 6/1958 and 6/1959,, 4,694 20ga A5 shotguns were produced.
So somewhere in that first year should be the production of your shotgun.

This info from 'Browning, Sporting Arms of Distinction' by Eastman.


I had no idea, I like to look stuff up and learn something too..