It is difficult to chart the appearances of Ultron. Some stories have him with a numerical designator (model number), and some do not.

The Ultron that appeared in Secret Wars had no designation save his ordinary nome de plume. (Within that story Ultron went through at least two different evolutionary structural design changes, one from being rebuilt by Dr. Doom and the other from being recreated out of thin air by Klaw. It's not clear whether or not Ultron considers these to be iterations of himself.

Ultron has appeared in at least one dream sequence comic, where he battled the Fantastic Four as Ultron-13. Seemingly, the writers forgot that this was a Dallas type story that never happened, because the next time Ulty appeared, (in West Coast Avengers he was calling himself Ultron-14. *tsk* Doesn't everybody know this crap?