Curio & Relic is defined as any firearm in the origination configuration that is 50 years old or older, OR- is on the list published by BATFE (all Colt Woodsman pistols, regardless of age) OR the curator of a museum has applied to the BATFE and they have decided that THAT firearm is a C&R. Any ONE of the 3 makes it C&R.
To be an antique, it must have been made prior to 1899, OR use loose powder and ball, and not be readily convertible to use cartridge ammo. Your TC Hawken 50 cal muzzle loader is an antique, even if made last year.
Trust me on this one- I have held a C&R FFL since 1976.
A Marlin 39A that is 50 years old- Curio & Relic firearm. Same rifle, 49 years old- firearm. But next year it will be 50, and becomes C&R. It is not the year the model was made, but the year THAT gun was made.
Serial numbers were not required on rifles and shotguns until 1968. In some cases, the year of production can be shown (Remington used a barrel code) In some cases, we can show that that MODEL was only made 1950-52. If you cannot show that the gun in question is 50 years old, and it ain't on the list by name, it is not C&R.