I was googling 'Peterson screw-in stems' and found your forum and this thread...so hopefully this is the beginning of a long and fun relationship.
I recently picked up a 1911 Peterson on ebay - it has a reddish-brown tenon that the stem screws on to. I can't find any evidence that Peterson ever did non-push stems - it wouldn't make sense, as such a stem would make it impossible to get the tenon past the trap to make the 'system' work. But I would love to hear the opinions of others.
I acquired the pipe because the seller described it as almost 7" long, which would have made it a great candidate for an amber stem I was going to try to match up with it. But it turned out to be a little over 3.5", so not useful for my plans.
I can't post a picture here for another seven days, but if anyone is interested in images, it's a recently-ended ebay auction for a 'peterson patent nosewarmer'.