"file is a 14 Accnts Transfer QB file and cant be updated or opened in anyother QB but 14."

If you are using either Premier Accountant or Enterprise Accountant, you can use 2015 for that activity. That won't upgrade the file for your client, when you give it back.

"But don't worry, you can still work on the Accountant's Copy using a different version as long as the gap between the versions is just one year, and the accountant has a more recent version."

From: https://quickbooks.intuit.com/learn-support/en-us/accountant-s-copy-passwords/use-the-accountant-s-c...

For registration on installation: As of May 2020, only QB 2020, 2019 and 2018 are "supported." The registration process involves putting in the License, then expecting the Intuit Servers to respond. They don't even use the same URL that older QB programs expect for the contact point. That's also why trial and education license is Product and License info without trying to register.

You might keep this handy: https://quickbooks.intuit.com/learn-support/en-us/damaged-data/fix-license-validation-and-registrati...

You might be able to call Intuit to get a Validation code, for the older program(s). This assumes you owned them, already.

The QB Community is at this link:

https://quickbooks.intuit.com/learn-support/us-quickbooks-community/misc/03/community-us