Nice display Leon-- at least one of those has found its way into my collection
You are correct-- blank backs are the most commonly found m101. TSN is the most common
ad back.
Unfortunately, over the years the pop reports have lumped so many different cards into the m101-4 category that they provide no meaningful degree of accuracy. Mostly blanks and Sporting News, but other ad backs as well. It's basically pointless to rely on them. As for sales, TSN backs and to some degree Famous & Barr have not moved much, which is why these Probstein sales caught my eye. As we know, sometimes collectors jump into new projects when they see a couple dozen offered at once--maybe that sparked the interest here. Similarly, maybe the guy who won them from PWCC two+ years ago got discouraged at not adding much to the set and just moved onto something else.