Bob D. said:
I don't think butting the two stops end-to-end proves anything either way. I doubt the end of the stop is ground to an exact dimension such that you can do as you have. If anything I would think they would be short so that if you did install them end-to-end on a rail they would not interfere with each other. Not sure why you would need to put them end-to-end anyway.
Put them side-by-side with the holes facing each other and see if they line up.
I see a Fastcap tape measure in your one photo. Are you using that in any way and how do you know it is accurate?