A Frank Zupo endorsed mitt is a new one for me, I'm sure. But, new signature or block letter name gloves do show up every so often.
Reserve or part-time catchers are more likely to have an endorsed gloves simply because the glove manufacturers had more
models than available catchers outside of first baseman. They could sign players for gloves from seven other fielding positions.
This Zupo Spalding was very likely made during the time of his playing career as it is in most cases of timing of production.
Hope this helps.
In line with this, I think there is an Eddie Fisher glove from the 1930s on ebay currently that doesn't fit to the 1950s=60s Eddie Fisher who
played. Anyone have any comment(s)?