Here is what I found for the 24 cards in Series #3 so far. It looks like the first print run has no letter. Those can be found printed either in Japan or Italy. In addition, I am finding print run "A" and print run "B". So I'm working on getting all four versions for Series #3.
I have every card from print run 'B' and every card but one from print run "A". I am missing 3-16 Hank Aaron from deck "A". For the first print run (blank instead of a letter) I am missing Aaron from both the Japan and Italy prints. I'm also missing 19 of the 24 first print run cards issued from Italy.
Here are the back variations I've seen. I have yet to check for variations on the front of the cards.
2-10 Daniel Moreton - 'A' and 'B' have added awards
2-12 Cornelius Warmerdam - 'A' and 'B' have different text and awards/records
2-15 Julius Erving - 'A' and 'B' have added awards
2-16 Hank Aaron - ??? I only have the 'B' version.
2-19 Phil and Tony Esposito - 'A' and 'B' have additional text
2-22 Irena Szewinska - 'A' and 'B' have a small title change on back; 'A' has 1978 awards - 'B' not? I will recheck this one
2-23 Steve Williams - 'A' and 'B' have added awards
2-24 Dwight Stones - 'A' and 'B' have additional text