It didn't even check my P5 serial or if it was installed. As long as you provide CL with a valid serial to upgrade from, they simply send you the P6 package (this may be the reason that the upgrade is only offered through their web store). Mine does say P6 Upgrade on the barcode, but I suspect that's simply for their own storage purposes. I suspect whatever's inside the package is exactly the same wether you purchase upgrade or full since it just didn't care to check for P5 in any way during installation.