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Todd SchultzAndy's right--there is no solid evidence that distribution of blank backs preceded that of ad backs. There is arguably some precedence for such conclusion--m101s. Mendelsohn advertised these, either as blank-backed singles or on an uncut sheet with your name on the bottom front of the sheet before The Sporting News cards were issued, albeit only by several weeks to a few months. It is likely that some of the other advertisers got their cards before TSN and that collectors got their blank backs before then as well, although there seems little significance to this, as the cards are the same but for the backs.
Here's a blank backed e135 and a common Collins-McCarthy, for those unfamiliar with the back:
