your support document says i will need to re-authenticate if there are more than one schwab files to

If you have separate accounts with separate logins, you should be fine. The problem comes up if you have one account/login, but use it in multiple Quicken data files --  that is what Schwab is blocking. This could cause problems if you have a test file, or you restore from a backup and switch between the restored file and your most recent file.

My understanding is that this is entirely a limitation imposed by Schwab; they required this limitation as a condition for allowing Quicken to continue to access their servers.  So it's not a limitation imposed by Quicken, nor a limit of the technology being used. 

This will definitely cause problems for some users, but unless Quicken can get Schwab to relax their security protocol to allow more than one Quicken file to log into the same Schwab account, that's the reality of the situation.