The point of copying the files is not for a backup, that's what regular, scheduled database backups are for. The file copies are just so that you have files to use should the system databases disappear completely. It doesn't matter if they're out of date, you're just using the file copies so that you can start the instance and then restore the latest backup.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability