Windows Licensing moving up and around with newer and older licensed disks.

I have a good source of Windows 7 & 10 Windows COA Genuine Disks from a vendor on EBay.  I have had successful installs of every license so far. I am wondering since I have two Windows 10 Disks about to be installed on two current windows 7 machines…..and one older Windows Vista for Business Machine that I would like to move to a Windows 7 Machine. Can I take one of the Windows 7 Licenses and use it to move up the Vista for Biz….to 7 or do I have to buy another license of 7? These are all full install disks I think they were for brand new computers and not officially installed? I assume all are legal since they come with genuine stickers and the vendor has sold 1k+ disks with great reviews. This is  probably a dumb question but as many of you know I will ask anything to verify with an expert. Spent too much time dealing with mistakes to know better not to.