rarest backs

[darwinbulldog]

Originally Posted by Seiklis

T215-2 Pirate
T213-3 Overprint
T216 Blank back
T205 Blank Back

Few more you're missing

Far as I know the closest you'll get to a rare T212 is the T212-2 150 cards but there could be rarer backs I don't know about

Thank you.

A T215 Pirate is almost as common as a T215 Red Cross, isn't it? That's why I left them off.

T213-3 overprint might be a good addition, depending on whether the comparison set is T213 altogether or just T213-3, but my inclination would be to use T213-3 since it was issued so much later, as opposed to just being a different style printed in the same year.