I have had QB Premier Plus Desktop and have several years of versions (2012-2018) on my desktop. So, I am able to open and work on clients files of differing versions.
I recently switched from Premier to Accountants Desktop 2019 and it is saying I have to update the client files to the 2019 version in order to work on them. Obviously, I cannot do that without the client purchasing a newer version (they do not want to). I am reading that they can send me an Accountant's copy, but it can only be one year older than the 2019 I am working with.
Welcome to the Community. I'm here to provide some insights regarding how Accountant's Copy works in QuickBooks.
Yes, you are correct. You can still open and work on the Accountant’s Copy using a different version as long as the gap between the client's and accountant's QuickBooks is just one year (given that the accountant has the higher version). Using an Accountant's edition allows you to install multiple versions of QuickBooks on your computer. This way, you can still work with those company files in line with your client's QuickBooks versions.
I got here some articles that you can refer to about this process.
I can share some information about your QuickBooks license.
If you canceled your Premier Plus subscription after having paid the equivalent period of not lesser than 8 months, you're eligible to keep your license and download software updates. Although, add-on services like online backup and all other inclusions of the Premier Plus package will be disabled.
Therefore, switching over to the Accountants edition should not affect or override any of your previously installed versions. You'll only need to make sure to create back up copies of your company files before performing multiple installations.
You may refer to the articles provided by my peer @BettyJaneB to guide you with your installation. Please feel free to get back to me if you have any license questions. I'll be happy to work with you whenever you needed me.