i don't pretend to be a glock expert, just a happy owner of many and i live in massachusetts...boston, actually.
i am delighted to know of these serial number checkers, but an easier way, as advised by my gun store of choice, four seasons, gave me an easier way...if the serial number begins with a "A", "B", "C" or "D" it is ok. i think on the ones beginning with "D" you need to check (as they may be close), but A, B, or C is fine.
as far as frame changes, i know they did two, first the finger grooves, and then they added the utility rail. in order to curb my glock buying i now only buy the ones i can find with both the rails and the finger grooves. it really narrows one's purchase options in this state with the silly laws. it is ridiculous that we can only purchase ones made prior to oct 21, 1998. i implore all glock owners to sell their pre owned glocks to us MA residents and buy a brand new one for themselves...but i digress.
hope that helps a bit.
...g.