The grading companies used to follow what the SCD Standard Catalog and or Becketts did in terms of variations but that obviously does not happen anymore.
Topps proofs tend to be blank bank, but the 60 Throneberry, as well as the Hadley and Cimoli have finished backs. Still I agree with you about not including it on master lists
From Bob Lemke's blog blog
https://r.search.yahoo.com/_ylt=Awri...HRoRUgHyqk.mU-
From Dave Hornish's great blog and article by Olberman
But if Olberman is right they would meet the definition of a variation held by some.. card changed by the manufacturer after printing started
https://r.search.yahoo.com/_ylt=AwrF...ciWJ1.Ww_SlUA-