From the bridge on which IC to Bern leave ZÜrich HB, I could see a third Tm III. But this one was (today) in a position impossible to take a photo of.
Entering Zürich HB with the IC from Bern gives a different angle and I could get the number of the third TmIII today, it's number 19. So the full list is:
Ta 974 98 85 5231 009-2 ex 909 98 85 5231 010-0 ex 910 98 85 5231 019-1 ex 919