The stuff catchers' mitts are made of...

Do you know what is used to stuff a catcher's mitt ? Well, I don't either, but being a brand new gloveaholic, I tried to get the answer to that puzzling question and, well, I stopped before I got too far because what I saw horrified me. I don't know how old my glove is, probably dating back to the 1940s, but I guess someone must have done something pretty bad to its guts. What I saw looked like the end of the sleeve of a cotton sweater...
Does any one of you have a plausible answer to my discovery, I don't know, maybe manufacturers had to use their own clothes to stuff mitts during World War II because of limited fabric supplies ?
Or does this mean I got my hand on a vintage bad quality mitt ?
In case this might help, the only thing I can clearly make out on the glove is a series of numbers : 60-4268 on the back of the thumb, and the word "sporting" partly erased by use and time above the pocket.
Thanks for your help.
Does any one of you have a plausible answer to my discovery, I don't know, maybe manufacturers had to use their own clothes to stuff mitts during World War II because of limited fabric supplies ?

Or does this mean I got my hand on a vintage bad quality mitt ?

In case this might help, the only thing I can clearly make out on the glove is a series of numbers : 60-4268 on the back of the thumb, and the word "sporting" partly erased by use and time above the pocket.
Thanks for your help.