I'd just like to mention that I don't see anything wrong with there being such a miniscule overlap of printed monsters. We were told ahead of time, and inside the book, that a couple of the monsters would be printed in other places as well. Admittedly, the back of the book is misleading, but whoever writes whats in the book and whats on the back cover are not the same person, so somewhere a miscommunication occured. It happens.
The thing I think is significant is, the "overlap" as its being stated here, is when there are two different stat blocks from Necromancer Games and WotC for the same monster. If the Juju Zombie in the ToH turns out to be different than the one we're going to see in Unapproachable East, that's overlap. If WotC decides to use the ToH Juju Zombie in Unapproachable East, meaning that they would have to cite it as OGC (which they are perfectly entitled to do, and have done before), then it's not "overlap" because its the same creature.
We knew, even if whoever printed the back of the book didn't, we knew there would be minor cases of the two companies having differing stats for the same monster. Fair enough, stuff happens. But at this point we don't know if WotC is going to increase the "overlap" or if they're going to use the "duplicate" monsters as their OGC ToH versions. Let's see what develops before we start throwing stones and forecasting doom.