I am not an 1851 fan, only have one. But I am aware of Ubertis with square and round guards, steel backstraps, brass back straps, steel guards, brass guards, barley corn sights, pin sights, square notched hammer, "V" notched hammer, safety pins on cylinder, no safety pins on cylinder, safety slot in hammer, no safety slot in hammer, shield cut for shoulder stock, no shield cut, backstrap cut for shoulder stock, backstrap not cut, and at least three different Uberti TMs. Right there, that is quite a few possible different revolvers. I am not sure if the front sights ever came in different heights (like on the original Colts), nor if the round guards came in different sizes. Also, not sure if the barrel lug had different shapes for the loading notch.
And then we get into finishes...
But, I think you see will need at least two different revolvers for your collection!
Fingers, or someone else who really knows replica 1851s, will be better able to give you the variations.
Kevin