There is some great info in this thread:
http://www.net54baseball.com/showthread.php?t=92743
That original thread got up to 3 pages long. I have a bit of new additional information that may help or may muddy the waters. Here is a new group of movie star cards I picked up. These came in a "Screen Star Subjects" pack but they are not square cornered as was reported for the 1949 issues.