Posted By:
CraigHi Jeff,
The most difficult back is easily the 'no-ad' back, found only in the first series (1-50) of baseball players. Each of the boxers (51-76) can also be found with this back variation.
I'm not realy able to accurately quantify the distribution of this back, but it is certainly quite difficult to find. It should be noted, however, that most T3 collectors over the years have paid little attention to the back variations when determining card value or desirability. Most have always been content to build a set consisting of one example of each front. Quite a task in itself.
As I've attempted to piece together a 'master set' over the last several years (complete at 250 cards), I've been able to accumulate 27 different fronts with the 'no-ad' back variation. As a note, I have 3 'no-ad' duplicates available if anyone has any they'd like to swap.
Lastly, I'd say the Turkey Red 'ad-back', found in the second series (77-126) is a bit more difficult that it's checklist back counterpart. Probably not as scarce as some might feel, but certainly in demand by collectors due to it's unique and attractive design.
Hope that helps.