My vote is for the 1942 Donora program premium that Lucas mentioned...but I would be open to calling the 1943 M114 (which I own) or the 1946 Propagandas or 1946 Sears PC "rookie" issues as well. Everything else is, well...close.
But because everyone has their own definitions of what constitutes a "card" or a "rookie", I've updated my "HOF Earliest" website to show everything that could fall into the realm of "rookie" or "earliest" for Musial. Feel free to reach out to me if you have any proposed edits or additions!
https://imageevent.com/derekgranger/...est/stanmusial
__________________
...
http://imageevent.com/derekgranger
Working on the following:
HOF "Earliest" Collection (Ideal - Indiv): 250/346 (72.3%)
1914 T330-2 Piedmont Art Stamps......: 116/119 (97.5%)
Completed:
1911 T332 Helmar Stamps (180/180)
1923 V100 Willard's Chocolate (180/180)