Have done some testing and observing on the bessie and avenger and have come to the conclusion that they both need to have certain parts to be able to exist or spawn in the enhanced version.
For example the Bessie will only spawn in the new game with the ‘Heavy’ accessory.
I’ve found 3 bessies and they all had this accessory. This explains why some bessies have come over and some haven’t.
Pic of a bessie from old game that I added the accessory to.
Now for the avenger from what I tested the avenger will only spawn/ exist in the game if it has the ‘Deathly’ accessory. This explains why my caustic and blast avenger didn’t make the cut.