Fred,
I do not believe that Mays was ever part of the Milton Bradley "Win a Card" game. I have never seen it on a checklist and have never seen it or heard of it in anyones collection. I have put together a few of these sets and this is the first I have ever heard of a Mays despite talking with people that have put together many sets. Some 1968 cards can be somewhat difficult to assess the bright yellow backs in the Milton Bradley cards vs. the golden backs in the first two series of cards in the traditional Topps sets. There are some cards that have backs that seem to fall somewhere in the middle of the classic colors. The best article about the game and set and even a possible uncut sheet (simulation) is at:
https://sportscollectorsdigest.com/c...on-bradley-set
I suspect that this is a PSA mistake. I have never seen or heard of a Mays in the set, but it is certainly not unheard of for PSA to make errors in labeling the cards they grade. If anyone could show a picture of the front of a 1968 Mays card that showed the white border from 1967 football or Topps Hot Rods then this would raise the question to another level. until then, I believe this is a PSA error and I believe that a 1968 Willie Mays Milton Bradley does not exist.
Rick Johnson