This is very true, as well as there being books from known pedigrees floating around that aren't identified as such due to them not having specific markings associated with that pedigree. For example, from all of my research, it would appear that right around mid 1943, the San Francisco pedigree comics no longer have the "Tom Riley" ink stamp on the back cover (there may be a few stragglers that do, but it seems to largely disappear around that time). Also, the penciled arrival date with cursive "Gilboy" G on the front cover, give way to a generic ink stamped arrival date around the same time. I believe that there are comics from that collection circulating that just don't have any markings to identify them as such. Other collections that were never established as a pedigree (such as the Chicorel collection, which yielded a Marvel Mystery #9 in 9.4!!!), were sold off in two or three batches, the first one or two of which being sold before the idea of a "pedigree" was a widely accepted concept. The comic posted below is being shared as an example of a book that's not considered a pedigree due to circumstance. I don't own the book. Trust me, if I did, you'd already know it!