You should archive files in PLA format. I don't know about AC12 files to be migrated -- I haven't heard that one before. Your problem is that the file you are opening in AC13 is reading it's embedded Libraries.
Look for an AC12>AC13 migration guide in your documentation for help on migrating files. Typically, you just open the file in AC13 and go to work -- you can unload the old Libraries and load the new ones (that's what the Migration Library is for) if you wish, but it's not necessary.
MacBook Pro Apple M2 Max, 96 GB of RAM
AC27 US (5003) on Mac OS Ventura 13.6.2
Started on AC4.0 in 91/92/93; full-time user since AC8.1 in 2004