I agree research is both fun and educational. But part of research is context. The Ball was originally part of a very large collection of balls put together by a collector who would travel to spring training and collect mostly rookies and prospects. I know this because when Sig Auctions sold the collection I bid on a few lots winning this ball and a few other items.
Many of the balls contained no star players because he wanted everyone on the roster anyone who collects autos knows it's the obscure guys that prove the most challenging this ball had a Henry Aaron. I owned a few Aaron Autographs but never a Henry. I fid some research and found both Red Sox and Braves on the ball. I later found that the Braves and Sox had played a 7 game series.
https://www.bdtonline.com/sports/bra...80a4b7f3a.html
So he had lots of opportunities to add to his ball. But my experience tells me that is is tough trying to get both teams as players from one team group together. It has been argued that the ball could ONLY be signed on one day March 10th... I would disagree as hanging around spring training you grab what you can when you can. If a game is going on you can get from 2 teams. But if you vist Red Sox camp on a non game day you can still add. And to me the definition of a spring training ball means signatures were added over the course of the spring. So maybe Morton was added on March 10th ...maybe.