We are using LanSweeper to help us determine what computers still have Windows 7 on them. Once we reload the PC with 10 or completely swap it out. How long does the old asset stay in LANsweeper? I see that several non present Windows 7 assets are still showing up.
It's all based on how you have your configuration set. Are you deleting the old PCs out of AD? There is a Asset Cleanup option called "Remove computers not found in Active Directory from the Lansweeper database." which I don't believe is checked by default.