Howdy Grizz,
The only 2nd Gen I have is an NRA Centennial, so I don't know if that makes a difference, but it has a two digit number on the loading gate. Neither of my third gen's has a number there, and my 1st gen has 3 digits. I think this is an assembly number and seems to me it matches another number stamped somewhere inside (have to pull the grip frame I think). I've seen it before but it's been a good while.
On the TV show Pawn Stars several months ago they had a nickled Colt from 1880's, and the "expert" (not the same guy they usually use for old guns) pointed out that the loading gate number was different than the other matching numbers, so this meant the gate had been replaced and somewhat lowered the value. Some "expert"!