His uni has one disc and pays quite a lot for the issue to the faculty of licensed copies.
I think that what you are describing there is the volume license agreement. The university (or other large organisation) obtains a specific release of the installation media for a variety of MS products (Select Agreement, I think).
This version allows multiple installations to be made using the same license key (simplifying management of a large number of PCs). The installation does not, normally have to be activated.
The organisation then pays MS monthly or annually for the actual number of licenses for each product in use.
How that is calculated and charged for is another discussion entirely - people make a living out of understanding volume license agreements!!
The point is though, that the installation media should not be copied (except for the purpose of backup), given away or sold, and neither should the license keys.
That is quite different to the OEM license, where each license is a separate entity, bought individually (although ostensibly with a PC or component). I am not clear about the relationship between the license and the physical installation media, as it is not always supplied with the license, as you probably know.
It is not possible to use the Volume license to install an OEM or retail version, and vice-versa.
SD