I agree with way nick says
compare it to sneakers. You go to the mall on a busy sunday. The day b4 some new gr nike af1 dropped but instead of getting the gr colorway that dropped you get the a tier zero edt that dropped the same day. The likelyness of seeing someone with the same shoe as you is highly un likely, yes u will see with an af1 but not the ones u got.
Now taking it back to tees, yes u can have the chance of running into some one with a diamond tee but with diamonds sales taticts, the chances of having someone with the same model tee is rare and then the chances of some one having the same color is very unlikely to happen.