Well, the cut down cavalry carbines shouldn't be hard to tell, but when you don't have a tape measure, 24" or 26" looks the same as 25"

The one at Tulsa probably had some damage to the end of the barrel or rust and was cut down by the Chinese to export, could have been real and just an odd barrel length but that's both unlikely and unprovable.

As to uncommon, rare, etc..... Opinions vary but in the last 6yrs of looking, I have found exactly ZERO! but at the same time I have come across several other "rare" rifles. Sometimes it's just luck as we have no idea how many survived. Like the Type I rifle, only 50,000 or so made and I find them on a regular basis since almost al of them seem to have survived the war.