They have repop'd/fantasy'd round and square and even double bubble versions. I recently sold a square Nesbitt's repop and inspected some round versions. That's why the back on the OP piece looks suspect to me. But as others are saying, what is the bigger concern is the face, it's apparently pure fantasy and confuses the issue of authenticity.
some of these werent used very much, they were in business until 1976 or so
they made a bunch for many companies so it is possible for one to have been made and not used
I would think all of the different angles in the backs of the square PAM bodies would be expensive to replicate, and in the same gold color
I have seen the new round bodies but not new square bodies that look original.
