Your serial # 1A-05016114 still follows the system used throughout the 80s, and apparently into the early 90s.
So that prefix indicates an amplifier manufactured in year 1 of the decade.
They even told me the color of my T40._________________Tony ITOC #05-000134 T-60s, T-63, T-15, Generation Standard, Hydra, Mantis LT, Milestone, Mystic, Odyssey, Patriot, Patriot tremolo, Predator, Raptor, Razer, Reactor, 3 Rockmasters, Tracer, Backstage, Bandit, VSS 20, Vypyr 30, Vypyr VIP-1.
I just want to make sure people understand that the date of manufacture given here for a T-40 is a pretty good estimate, not exact.
The Schmidt Serial Numbering head didn't have the capability of letters, only numbers, so there would have been only a very few with the 8Mxxxxxx.