Software

As far as I know, those licenses are good for the installation of Windows on one computer at a time. Just like if you were to buy a copy of Windows, its completely legal to reformat and reinstall it. It is illegal however to install it on another machine. I think as long as that license is not used in two places at once then it is a legitimate usage of the OS. Thats my take on it at least. Rules may be different on a large scale like that... or a corporate scale for that matter. However, if you cross the single user rules over to a multiple user scenario, I think its legit.

If the stickers are on the PC they are probably OEM licenses that were originally purchased with the PCs. OEM licenses are "bound" to that PC. If you sell those PCs, the license legally MUST be transferred with the hardware.

Assuming that they are OEM licenses, there would be no problem re-installing the original OS and selling those PCs with the licenses included -- in fact, it would be illegal for your company to keep the OEM licenses.