Well, there's what Beckett says is a rookie, and then there's what really is a rookie. In terms of "pre-major/modern release era"(basically '47 and earlier) Barring complete obscurity, I view ANY Major League release, regardless of major or regional release status, as rookie cards..
While I'm willing to "accept" the 1948 Bowman('49 for Kell) rookie designation for these players(forgive me if I forgot any), the Berra, Spahn, Kell and Kiner to me all count as "true rookie" cards in the '47 TT set..
The listing of guys like Rizzuto and Feller(probably a few more) as RCs in '48 Bowman, is a complete and utter joke. Those type players deserve NO rookie designation in the '47 TT set, just because they fall before the '48 release.
Again, I'm willing to forgive(and accept) some of the Beckett player RC designations for '48-49 Bowman, but some are so far off, it's not even funny..
For better RC acceptance and designations, ignore Beckett, and refer to Phil's lists..
http://www.net54baseball.com/showthread.php?t=141603
http://www.oldcardboard.com/ref/rookies/rookieslist.asp
http://www.net54baseball.com/showthread.php?t=128179
While, I and others, are willing to give some lee-way to later releases than those on these lists(I'll refer to those as "acceptable rookies"), Phil is spot on, in regards to "true rookies". Although, there is still some debate as to what are cards.