Environment Refresh: Destination Environment's Users not getting overwritten

Summary:

Hello - Whenever we do a P2T, our understanding is every user from the Production environment (source) will overwrite all users in the Destination environment (Test). We currently have some fictitious users in TEST (i.e. Iron Man, Cinderella, Captain America, The Hulk, etc) that we use the test downstream applications.

What we noticed is AFTER a P2T refresh, those fake users are still in the system. My question is….during a P2T, does the Destination environment's (TEST) user list get completely deleted, and then PROD users are imported? Or, are prod users "pasted" into TEST and if there are matching users, data gets overwritten but any non matching users remain intact (i.e. my fictitious users above)