Lenk's book is considered the definitive work in this area, although there is one signed gun that he didn't have access to that changes the date by some years and a couple of the gunsmiths involved have similar names and overlapping dates. Having read though the book, I find the discussion of actually defining a "flintlock" to be a bit arbitrary as there is a rather clear evolution of the flintlock from other lock forms so it's not like there were no flintlocks of any form and a gunsmith had a revelation on Tuesday morning, October 28, 1627 and built the first lock that afternoon. We'll never know the date of the first flintlock. The best we could know is the date of the first known "surviving" flintlock. Maybe Gary will tell us what date Wallace now things is correct?
Tom