I think I went beyond the outer layers. I FMQ'd a 4x5 inch sandwich. I can't tell if it's waxed as some have asked. It unspools almost like fishing line if you can picture that. Very stiff. I thought it made nice stitches, they were very prominent since the thread is a bit thicker. But I don't want to cause problems for myself if this is not a good idea.
I did google around for reviews of this thread before posting here but as MadQuilter alluded to, the stuff for sale looks totally different from mine so I wasn't sure if it was the same thing. Googling for vintage Star thread just brings up items for sale.
I think I'll take a picture of the thread unspooled so maybe you guys can get ideas. I do worry that it's hand quilting thread.