Everyone understands that the census isn't 100% accurate. Just because a measurement isn't 100% accurate doesn't mean it's not valuable. I know this is the CGC forum and there are people with pitchforks at the ready if anyone dares make an error (OMG, CGC MISSED TEH RESTORATIONZ! BURN THEM TO TEH GROUNDZ,) but I don't subscribe to the idea that something has to be a model of purity for it to be valuable. I mean, every measurement has some error baked right in.
So for me, even if the census is 20-30% inflated by resubs then wouldn't that inflation spread itself around across titles, normalizing the data in a relative sense? If it does, then I don't really care about the inflation since knowing the absolute number of graded copies of any book isn't as interesting to me as knowing the relative scarcity versus books from the same era.