InDesign CS3 spell check would not check part numbers but CS5 does

I am running version 7.0.4. (mac version) We used to run CS3, which automatically skipped over part numbers.  Now CS5 stops on all part numbers.  I understand the GREP "no language" trick.

I am wondering if there is a solution that does not involve a GREP.  Why did CS3 have no problem and CS5 now stops on all part numbers?

Any ideas would be appreciated.

Thanks!