The key is the data folder. Each user has a Notes Data folder which contains their settings. On the old PC, which was XP and had migrated from 6.5 -> 7 -> 8 -> 8.5 this was at:
I installed Notes 8.5 on the new machine and copied the data to:
Selecting to overwrite or replace all conflicts. I then started Notes, cancelled a few meaningless wizards and messages (one about "Internet Mail", one about "IM" and a "Cannot create folder").
However after 15 mins of Notes "churning", I can see my inbox, and I'm migrated.