No, mechs in years made before the bushing was added have a larger-diameter bolt, the one that threads into the cage. The part of the head of the bolt that goes down inside (I think it's called a journal bearing in mech-E speak) was larger by the thickness of the plastic bushing, because the hole in the aluminum knuckle is the same on both. So it's the bolt that determines whether you need a bushing or not. Put another way: if there's room for the bushing, then you need it. If you have the no-bushing version of the bolt, then no bushing will fit.
If there's a small amount of slop from wear, then you might wish you could stuff a bushing in there, but there's never going to be
that much wear — I hope! I don't think there's ever any question, it'll either be a close fit or a
way loose floppy fit without the bushing. You can however add a bushing if you also replace the bolt with the later one, with the smaller journal.
I'm surprised to hear that a '71 has no bushing, I would have thought the no-bushing mechs were older than that, like old enough to not have a Patent date on top. Certainly by '72 they had bushings.
EDIT: Hmmm, the
Campy timeline here says the plastic bushing was added for the '73 model year. My memory needs recalibrating.
Mark B