In the wood 8x10 film holder I got with that camera was a sheet of film. I noticed it when I started pulling th dark slide. So I went and developed the mystery sheet knowing at least that part I exposed would be blown.

That part I exposed was blown, and the rest was not as exposed but there was nothing of an image. Darn. But I noticed the two square notches and I had not seen that before. So a bunch of Internet searches later and then looking at the edge of the film in better light - it's Ansco Safety Film. Thick stuff.

Kind of neat there was an old sheet of film in an old wood film holder.