Posted By:
Tim NewcombHi Darren,
There have been a number of threads on the topic of M101-4 backs over the years, which you can probably find using the search function.
I've been collecting this set and M101-5 very actively for a while and have over 300 of them. The blank backs are by far the most commonly found in both sets--more common than any ad back. They are definitely legit, however. I'm sure they were sold to various advertisers who chose not to pay to have their name imprinted, but still wanted to distribute the cards with their products.
The Sporting News backs are among the more common ad backs, but not as easy as a lot of people think.
Feel free to Email me with any other questions or comments.
Tim Newcomb