You can't really scuff the base and clear over it at all, the clear will magnify the scuffing. If you scuff you MUST apply more base prior to clear.
But FOLLOW THE TECH SHEET! Many bases have warnings IN BOLD PRINT do NOT sand the base! It will clearly say things like "nib" it or "Scuff" it which is NOT "sanding" it flat, that is two totally different things.
Read the tech sheets!