Well I lucked out here. Though I did pull the SSD used to test the 800G1 units, I had not yet repurposed it or reformatted, was still in my small stack of SSDs ready to be reused. Only question was now, which of the two units did the drive LAST come out of? I couldn't remember so I imaged the SSD to file in case my first pick was wrong. Windows 10 loaded and was still activated on #1. Interestingly, I restored that image to a 2nd SSD and installed it in #2, it loaded and remained activated as well!
Both systems were identical enough same BIOS version, CPU, and graphics, only exception being one had 16GB vs. 8GB RAM, and the different SSD drive make and models (same capacity though).
Per the post by Kaido citing the
Microsoft article on activation, in order to get Windows to report the needed "Windows is activated with a digital license
linked to your Microsoft account" in order to preserve activation after a reinstall of Windows, it is NOT sufficient to add a Microsoft account to the PC to be used for things like email. e.g. as displayed in Settings -> Accounts -> Email & Accounts. When a Microsoft account is added here, it will be shown as one of your devices in the online Microsoft Account (profile), but will NOT be reported as 'linked to' in the Activation section of Windows Settings.
You have to go the full monty and enable signing into the PC with your Microsoft account as well. i.e. NO local account. Will be testing some other scenarios this weekend.