[Leon]

After some more research I am not so sure "521" ever had to do with the number in the T206 set. I think it is possible it was a coincidence there were close to that many in the set. Here is a March 1938 Card Collectors Bulletin, and one of it's pages. with reference to "521" and there being around 510 designs.
Also, this 1942 Edition of the Card Collectors Bulletin Checklists lists "521" and then has 522 cards listed, for the White Borders (*and has T206 handwritten in, which is the earliest reference to T206 I can remember, assuming it's from 1942-1943..).

.

Originally Posted by toppcat

Card Collectors Bulletin of April 1, 1953 has a lead article entitled "Is T206 Complete at 523 Including Magie?" It states "The checklist of T206 was originally compiled by Mr. Howard M. Myers in May of 1938. That was more than fourteen years ago and in that long length of time there have been no additions made to the original checklist."

So this gets even more mysterious if Myers had 523 in his checklist but Burdick only had 521, then 522 in the ACC, why was there a discrepancy?

I thought I had a copy of Egan's list but can't locate it right now.