System File Checker (SFC)

I have a question regarding the SFC /scannow command.

If the original CD that came with the computer is Windows XP SP1 and the machine now has SP3, when I run SFC, a damaged file on the machine should be replaced with a good file from the CD BUT the files on the CD are obsolete since they are from an earlier service pack. How does SFC handle this?

In other words, does SFC have to be run using only the SAME version and service pack CD as the version installed on the machine?

Appreciate any pointers.
Thank you, Jay