There is a P on the left side of the receiver, but I already checked for a tag and found none. Cool story though about your friend. I was planning to do that myself, but without a tag it's more than a little impossible.
It's a real shame when those get lost. My buddy is one of those guys that's too lucky for his own good. He got the chance to jump on a completely unused, un-issued K31 at a time I just didn't have the money. Not to mention some others lucky finds.
Still, get the K31. You won't regret it! I love the look on people's faces who haven't seen a straight pull rifle before.