Now that's good data. I learned that Nicholas Flamel (1340-1418?) accused other alchemists of using blood so it was probably well-established as you describe by then. However we have many Biblical and mythological hints that everyone always knew blood was important. Noah prohibited eating blood (hinted in his account and supported by Acts 15), indicating that there was also a prediluvian practice about it that has a bit of continuity with the first century. It seems to me that cannibalism never was a tremendous subset of the depravity though, until recently as you hint; the bigger deal was for a much longer time the mere destruction of the child as a substitute, typically by fire.

But there could be very much study done on the "drunk with blood" concept and that might inform how it led to this special appeal to the anemic. I wonder how much of this can be pinned on Vlad and the vampyrs, as they are right in your period (c. 1430-1477).