yes, I would have trouble to move out of the pin, but I would still have no need to tap?
It's already been said, but I'd like to add to the idea that it doesn't need to hurt to be effective. Also, Ikkyo is a tough pin in my experience. With senior deshi I'm pinned pretty well, but against many other people I usually feel like I'm not completely immobilized, although I'm well behind in position/timing. I usually tap when I sense some degree of this, based on who I am training with...although I prefer the nice stretch that comes from a good pin (ikkyo in particular is great for fixing any neck and shoulder aches I might have) so I try to wait for the need to tap, but if it doesn't come and I can't tell any technical poblems to suggest, I tap to move on. Often, tori will ask me to try to get up in order to check themselves. As uke, I'm always trying to enter through the connection though so it's usually obvious to both people how much slack I have...
...perhaps, to some degree, if tori doesn't know the pin is insufficient, it's because uke isn't applying themselves properly. On some level we have to let tori do the technique, particularly if they have something definite to work on, but if uke is applying the proper pressure, it should be somewhat obvious to both parties I think.