The automated agent could not verify the installation and forwarded me to a live agent who escalated me to level two. That agent remoted in and activated me using a retail key.
Neither of the two different agents that I talked with ever questioned my right to run two instances of Windows 10 on the same license. They just addressed the technical problem. Apparently there are still activation bugs, because I wound up with the retail key in the second installation.
Both of my installations were 64bit, but it would have to work the same with 32bit and 64bit because the license is agnostic to bitness.
You are going to have to come up with the quote for that because that is one subject that is always discussed in the forums and yet this is the very first time that anybody has ever expressed this very unique concept. If true, then it will be a game changer for literally millions of people and Microsoft would stand to lose quite possibly billions of dollars. We are all waiting to hear back on this.
The key change is that the device is activated (the mobo is the device; the license is written to the firmware on it). Any copy of the same edition should activate on it since a clean install checks for a license in the firmware. The ticket generated by the first upgrade writes the license to the firmware and there is no further checking for a qualifying OS. Also the resulting dummy product key is always the same, so there is no futher need to verify that either.
Also, even if this DID happen, it would only be true of OEM preinstalled Win8.1 systems. My system, for example, is not UEFI and was not OEM preinstalled. So, I'm certain there's nothing in the BIOS firmware of this machine that MS can change.
What is recorded on the MS activation server is a hardware hash that MS generates -- which, together with your original OS product key, uniquely identifies your machine (or, so I've been told). The motherboard is the part of that hardware hash which, when changed, tends to indicate (to MS) that you're now using a different "device".
1. Read the EULA. The EULA definition of device includes partitions. Two partitions = two devices.
2. There is no license information written to a motherboard's firmware by any version of Windows. There is no "ticket" written to firmware. The manufacturer can put a product key in firmware for Windows 8/8.1/10 to read, but that is it. The hardware information and activation information ("license") is stored by Windows 10 on Microsoft activation servers, not motherboard firmware.
Every time Windows 10 starts it surveys the computer's hardware and runs a whole bunch of things through a formula resulting in a Hardware ID. The Hardware ID is stored in a file on the hard drive. As long as Windows 10 computes the same Hardware ID because no major hardware changes have been made, it stays activated. That has nothing to do with any "license" stored in firmware.
The initial upgrade to Windows 10 from a previous OS will create a ticket file stored on the hard drive and that ticket file allows Windows 10 to push a new activation and hardware ID to Microsoft activation servers during the upgrade activation process. The hardware ID is also stored in a file on the hard drive for future comparison.
When a major component, such as the motherboard, is changed, when Windows 10 does the hardware survey at startup it will create a Hardware ID that is different than what it has stored previously on the hard drive and will deactivate that installation of Windows. Then it will attempt to match the newly created Hardware ID with one stored on Microsoft activation servers - and finding no match, it will prompt the user that Windows 10 needs to be activated.
The previous OS product key is stored in the Windows 10 registry if it is an upgrade - but that is only used for rollback back to that previous OS purposes.
One way is to fit a hard drive caddy into a 5 1/4 external bay and keep the drives outside the case. That way, only one runs at a time and you can have as many operating systems as you like without them interfering with each other.
All of this is just academic because it does not address the OP's original question, which I think was already solved for him. The question dealt with what he considered to be a corrupted system, which we explained to him was not corrupt. Because the OP is running two separate instances of Windows, he can not access the programs that are associated with one installation of Windows while he is running a different installation of Windows. As far as the whole question of licenses and dual booting on one license, there are plenty of threads here at the forum that already deal with which we can use to carry on this conversation.