Those almost certainly were state requirements. IIRC, in order to hunt Pennsylvania's muzzleloader season, you have to use a flintlock. (Thus Thompson-Center's fiberglass stock, stainless steel, flintlock Hawken.) (I was told that Colorado's muzzleloader season almost had the same requirement, but the Department of Wildlife or whatever it's called asked a bunch of guys who weren't rigid traditionalists before they asked the ones who demanded that your "garb" at "rondy" be hand sewn from fabric hand spun and woven at home...)
Correct on the muzzleloader season, and yes, I was referring to PA specific regs.
At one point I had a T/C Contender with a stock/forend and a 16" (with muzzle break) .45-70 barrel. At one point it wasn't legal for me to use up there for deer hunting, again IIRC.
In the case of the flintlock requirement, that was partly due to an attempt to restrict the season to purists. Deer hunting in most of PA (at least back then) is nigh unto a religious event. The first day of buck season (only two weeks long, and half the deer dropped in the 1st half hour of light on the first day) was officially no school where I grew up. If percussion muzzleloaders were permitted, that would require another school holiday.
Buck season consisted, if you didn't tag one at daybreak, of a sea of orange-clad chaps wandering about, pushing the same group of 6 does (no buck) from orange dude to orange dude like a pinball.
The populations are higher now, and it appears much regulation has been liberalized, so to speak.