The biggest problem that pre- (and indeed post-) 2015 RDs suffer with is wear in the o-rings that set the float of the top pivot bolt.
Assuming the hanger is straight - and don't assume, measure - any excess angular movement of the derailleur relative to the upper pivot will lead to poor shifting.
Typically, this wear and tear is grossly accelerated by lots of volatile lube being sprayed about in that area of the bike - stuff like WD40 and any mineral-oil based lubricant in a spray can will find it's way into the upper pivot housing and eventually degrade the material of the o-rings (hence the recommendation in Campagnolo literature for synthetic lubricants).
It's fixable by having anew top pivot bolt assembly installed by a SC. We (and one or two of the other SCs - it's not a Campag requirement that we do) also keep a range of o-ring sizes on hand so that if the wear and tear in the upper pivot sleeve itself is excessive, it can be dialled out with new o-rings.
What bikerjulio says is true, I do deal in fine degrees of perfection. All this kit costs a lot of money - it should work to spec - otherwise what the hell is the point? Otherwise we might as well not bother trying to develop better shifting, braking, etc because it all *works* already and works better than most people are ever going to need, in a functional sense ... and has done since time immemorial! The point is, part of what all of those pounds, euros, dollars or yen is buying, when you buy top end cycling equipment, just as when you buy top end hi-fi or cameras (my other two obsessions), are incremental improvements on something that is already so far removed from simple functional norms that to talk in terms of stuff "working" becomes non-sensical. We are talking about "working as designed" which is something totally other.
That and the fact that I am a pernickety so-and-so ...