It's no surprise that there wasn't a Topps card of Willie Mays in 1951 despite the fact that he was the NL Rookie of the Year. He actually spent the first part of the season playing for the Minneapolis Millers. In fact that is mentioned on the back of his 1951 Bowman card. The Bowman cards were printed in seven series with Mantle and Mays rookie cards appearing in the final series which came out in July. Topps of course, had only 2 series. I'm not sure when they were produced but with a total of 104 cards, it's not surprising that several notable players were absent.