Well, Phil, gotta go ahead and disagree with you there. Here's a 1949 Philadelphia Bulletin rookie. Per the Standard Catalog: “Each Sunday between May 22 and July 24, 1949, the “Fun Book” rotogravure section of the Bulletin included a page of (usually) six baseball cards of the hometeam A’s and Phillies...” So this definitively dates to some time in the early part of the 1949 baseball season.
And yes, there was an Ashburn rookie too:
