Let's Reword this to match Intuit Terminology:
QB Accountant (no longer has the word Premier in the product name)
Enterprise Accountant (can work with Accountant's Copy from Pro/Premier or Enterprise)
All Accountant Programs work with their specific Accountant's Copy, and from the same year or one year Older than their Accountant Programs.
Can Convert the .qbx to .qba. A = Accountant, to work on that Divided subset file. Then, when they are done, they "save out Changes" creating a .qby. The QB user who sent the .qbx gets back a Changes file to Import. In that meantime, they had a notification that their own working file has Restrictions on it.
It's a data swapping Function that does not involve the QB user required to Stopping Work, waiting on the Accountant to provide a replacement file.