No, I mean universal IEM's of every custom IEM.
"If UM Mages are customized for two different people will they still sound different?"
Ultimate Ears say, if you buy a UE11Pro 4 years after your first one, it should still sound exactly the same as your last UE11Pro.
Now... if custom IEM's sound slightly different from person to person, they shouldn't, but if the laboratory is lazy or rushed then they probably will.
Ideally all CIEM's should be tested for uniformity, that's why they send you a frequency response print-out sometimes.
Thousand Sound say they spend up to 2 weeks making/testing a single CIEM.
What I meant by they all sound different is I mean every custom IEM will sound different to the next one, just like universals all sound different to the next one.
What universal and custom IEM's have in common is that almost all of them use the same balanced-armature drivers from the same two companies.