You may be able to do it technically, but it would provide false and wholly unreliable conclusions because until recently, PSA lumped them both together, along with some others that had different advertising backs. The fact that you might see some entries for a player with "blank Back" notation does not mean the 12 other examples listed for him without such notation are all with Sporting News backs. IOW, a player with a certain number graded "blank backs" has at least that many with blanks but does not mean the others graded for that player without the notation do not also include a large number of blanks.
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Now watch what you say, or they'll be calling you a radical, a liberal, oh, fanatical, criminal
Won't you sign up your name? We'd like to feel you're acceptable, respectable, presentable, a vegetable
If we are to have another contest in the near future of our national existence, I predict that the dividing line will not be Mason and Dixon's but between patriotism and intelligence on the one side, and superstition, ambition and ignorance on the other.- Ulysses S. Grant, 18th US President.
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