Actually a great part of comic lore!
Jerry DeFuccio the former editor at Mad Magazine was a rabid collector and comic historian. He made a life's work of seeking out professionals and documenting their contributions. He was a major contributor to Jerry Bails Who's Who. He was also a dear friend.
In the early seventies Jerry found Fred Guardineer working for the postal service on LI in NY. Guardineer recounted how he had answered an ad for DC and was given some assignments. Sadly, he rarely got paid! However, with aspirations of working as an illustrator, he realized he needed a portfolio and published work to add to his resume. He continued to work at DC with the condition that selected covers be returned so he could create a portfolio. He kept that portfolio all those years.
Jerry told him he could sell them for him if he liked and he agreed. The art was split between two collectors. Eventually, I acquired the majority of them.