I have been reading these T206 Sovereign threads and feel the need to respond.
First and foremost, just because a grading company has not graded a confirmed T206 front/back combination doesn't mean its unconfirmed.
According to Scot Readers "Inside T206" book he estimates that T206 production was approximately 370 million cards.
As of today PSA has graded 200,660 T206 cards, some identifying the backs and many others without a back designation.
This represents ONLY 5.42% of the estimated T206 population.
Furthermore, SGC has already graded a T206 George Davis with Sovereign 350 back according to their population report.
So to suggest that SGC has made an error just because certain collector/collectors cannot locate one is simply idiotic. Eventually other T206 George Davis with Sovereign 350 backs will appear. Just be patient.
The T206 resource checklists were a labor of love by myself and others for over 35 years. While I cannot specifically remember where every front/back combination first appeared I feel very confident with my research.
Enjoy these cards.
Art Martineau