From the convoluted world of Microsoft licensing:

If you want to “reassign” Windows desktop operating system volume licenses to other devices, you must have an OEM license with pro or better on the new (and old) device AND have active SA (Software Assurance).

What do I mean?

Volume licenses without Software Assurance behave like OEM licenses in regards to which device they are assigned/licensed. Both are only good for the device that they were initially installed on. If that device dies or is otherwise lost, the license dies with it. Among other benefits, Software Assurance allows you to “reassign” the volume license instead of purchasing a new license for a new device.

-For Example-

With Software Assurance

If you have a Windows 7 Pro OEM license that came with your Dell Optiplex 390 AND you have purchased volume licensing AND have maintained the software assurance, you can use the same volume license by reassigning it to a new Dell Optiplex 7040 (that comes with a Windows 10 Pro OEM license) when retiring the Dell Optiplex 390.

To further illustrate it- If you had a pool of 100 volume licenses and you refreshed/replaced 100 Dell Optiplex 390 computers (which all had those volume licenses assigned to them) with 100 Dell Optiplex 7040 computers that each came with Windows pro OEM licensing, you would not need to purchase 100 new volume licenses; your Software Assurance gives you the ability to reassign those initial volume licenses to the new Dell Optiplex 7040 computers.

You just keep maintaining software assurance and you have the same number of licenses.

Without Software Assurance

With that same pool of 100 volume licenses and 100 Dell Optiplex 390 computers, without Software Assurance, you would have to buy 100 new volume licenses to cover the new Dell Optiplex 7040 computers, if you wanted to use volume licensing with them.

-Some Gotchas-

• This does not apply to “Home” versions of Windows desktop operating systems; you must start with Pro or better.
• Your Software Assurance agreement has to be current when the licensing is reassigned.
• Both the old and new computers must have OEM licensing already in place, prior to “reassigning” your volume license.

-Disclaimer-

This post is only meant to be used as a guide. Please consult a certified Microsoft partner or Microsoft, themselves, when determining correct licensing practices and needs.