Taken from another thread explaining date codes:
Originally Posted by mojo100
I thought adding 60 to the code was not a reliable way to date the rifles. Has that been proven incorrect now? It would be nice since it's a good way to date stubs and rifles.
I don't recall who said that wasn't a reliable way to determine date of manufacture. I've heard the same.
Over time I've become convinced that the Bulgarian two digit code does match up to a year. Current Arsenal semi-auto US market rifles have two digit codes that do match up to a year.
Here is an Arsenal model offered in 2014. There is a two digit code 54.
ARSENAL SLR-104 UR 5.45X39 KRINK Factory SBR New : Short Barrel Rifles (SBR) at GunBroker.com
37 code on this SLR-95 would be 1997. These were on the market in 1997 so it seems quite logical.
Arsenal SLR-95 AK-47 Rifle, 7.62 x 39mm, Used : Semi Auto Rifles at GunBroker.com
I'm not sure when Bulgarian began using the two digit code - for Bulgarian military firearms the earliest two digit code I have observed is 15 (so far).