rarest backs

[darwinbulldog]

If we limit it to cards that have a cataloged front, comprise less than 1% of the cataloged set's total population, and of which fewer than 50 examples with the rare back are known to exist, what should we add or subtract from this group? (Let's also omit the blank backs and supplements and blue Old Mill for now.)


E98 Old Put
E121 Kings
M101-4/5 Everybody's, Haserot's, Holmes to Homes, Mall Theater
R316 Douglas Park, Morton, Rialto
T206 Old Mill (brown)
T206 Lenox (brown)
T206 Broad Leaf 460
"T206" Ty Cobb
T207 Red Cross
T213-3 Overprint
T216 Virginia Extra
W514 Hendler's, Barker
W515 Fleer, Jersey
W551 Wool's
W573/E120 Cafe du Monde, Cream Nut, Kings, Leader Theatre
W575 Johnson, Haffner's, Clark's, Gassler's