You can add a field to a table, and set it to "not null", even if that
table already has data. Ok. Backup that database, and you cant restore
it because that "not null" field containing nulls. If you use the switch
of gbak to skip data validation, you lost _all_ your checks (not only
problematic ones).
If live database can contains nulls where it shoudnt be, then backup
should restore database exactly as there was before backup.
Or, at least, no restore only that problematic checks.

Maybe you have a better solution? I'm waiting to read it! :)

--
Jorge Andres Brugger