I wouldn't be surprised. However:
1) It's a lot more likely that PN is on the spectrum between VdB and Violette Soleis/Noire de Barbentaine. The biggest brebas can strongly resemble VS. The leaves can resemble some strains of VdS, but not the main type.
2) It sounds like PN is more acid than IB, and this has never had honey, or intense sweet jam at the end of the fruit. If one manages to get fully ripe PN at the end of a sunny week, it will be pretty sweet, but not quite a sugar bomb. Flavor is intense, and sounds more complex in taste than descriptions of VdB. The primary feature that makes it really good is that it can be enjoyed fairly unripe. Heat is required for superior fruit, and is less tolerant than VdB of cooler weather (or dry weather).
3) The leaves of IB are far more rugose than that of PN, and PN has never had a tendency for red tips or stems. Now, I think I've seen a VdB (delivering fruit of roughly the same qualities of my PN at the time--mostly rotting but same general flavor otherwise, too) at an old farm, and the leaves there are much more rugose than most pictures displayed or my trees. If I may suggest, that tree is in full sunlight. Perhaps you could get better long term growth by keeping IB in pretty heavy shade for five or so years? PN does like some shade and is easily water distressed in full sun.
I've heard tell that recently, Mike McConkley is very agnostic about the distinction between PN, Negronne, VdB.