Questions: BackUp Exec 2010 R3 (pre)SP3

My company has 2 backups. One runs without errors and the other did the same until about a month and a half ago. Now it never passes verification. I know that the SP3 is a fix but why all of a sudden did it start failing? Are updates running automatically without our knowledge?

Can we restore from the backups that are there now after we install SP3 or will those backups be no good once the installation is done?

Also, why is it that the other backup has not failed yet? It's running the same version with the same OS (Windows 2008 Business). I'm just curious to know if we should be cautious about SP3 doing the same thing eventually.