Well, there goes the My Maryland theory.
However, I would not be so quick to dismiss the notion that there were other productions that starred a “Jane Stanwyck”. Walloon has done some excellent research, but s/he discounts the possibility of missing records, a “Jane Doe” marrying a Mr. Stanwyck, etc.
Regardless, the idea that all the records of the many productions that took place around the turn of the century are easily accessible from the internet (or anywhere, for that matter) is rather unrealistic. Poking around a bit I’ve already found one production in Boston at the Castle Square Theatre in 1902 (not a rinky-dink place, by any measure), but no cast list. Doubtful it could be found anywhere on the net. And considering the multitude of actors and actresses that have plundered the stage over the years, it’s most likely that only a small percentage are accountable via the internet. (I know a few working today on stage who you couldn’t find without poking them with a big stick.)
I know this probably goes without saying, but Broadway isn’t the end-all-be-all of Theatre. There quite possibly could have been dozens of productions of Frietchie in New York, Boston, Philly, D.C., etc. in the few years following its debut, and perhaps several large enough and “important” enough to merit a playbill sitting in Belasco’s office.
Here’s another idea if you’re really serious about this – call Amherst College. Fitch is an Alum, and they have a large collection of his papers, first printings, etc. Someone there might be able to help you on your quest.