i would not say rookie per se. Not until we find an uncut sheet or checklist that we can date to 1939. This whole 1939-46/1947-66 thing is an artificial construct that took hold as cataloging cards began in earnest but is demonstrably wrong. This uncut sheet of Exhibit cards is 1960 or 1961 at the earliest. Rocky Colavito is shown with Detroit, where he went after the 1959 season in a trade for Harvey Kueen. Next to Rocky is Ted Williams' Salutations card that supposedly was printed from 1939-46.
The dating divide likely stems from product redesigns after the war moving away from the Salutations design, so I give them a bit of a mulligan there. However, the reality is that ESCO issued the same card for years, hence the 1949 ("An Exhibit Card" legend on front) Salutations cards, the "Printed in USA" Williams Salutation cards, DiMaggio, Feller pitching, Tommy Holmes, and some others too. As long as the guy stayed in the show, so did his Salutations card.
Dating this stuff is subject to all sorts of poor inductive reasoning. There was a huge debate/discussion on the pre-1980 page recently with an unknowledgeable person pushing the theory that Willie Mays's first ESCO card was made in 1951, probably because he accumulated several of them and was trying to gloss them to get a payday. The refutation of that theory in part was the existence of a checklist promo card which does not have Mays on it. One of his proofs was the presence of an 1951 patch on the jersey. Well, the only deduction to make from that is that the image was taken in 1951. The card could have been made any time after the image.
My hypothesis, FWIW, is that the Williams would have been a 1940 issue at the earliest. Unlike today, ESCO was not trying to generate a buzz with rookies. From what I can tell, a rookie who made good (and Williams was one) might be in the next year's set, but not in the set issued the year he was an untested rookie. That Mays discussion was an example.