On Windows XP with SP3 that registry may exist. I'd have to boot into my desktop XP (dual boot XP SP3 - Windows 10 Pro) to see sometime, but in Windows 10 registry, there are those 2 spots I mentioned above.
It hasn't happened for a long time, but when Windows 10 did a major update, it saved the old Windows as Window.old (find using show hidden files) and it obliterated the HKEY_CURRENT_USER\Identities completely, and oddly enough in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Outlook Express it doesn't completely delete it, just some of the registry entries, and especially the one with the KEY and to the right shows the actual key code used to activate that program OE6 that I paid $5.00 for a long time ago. I'm still able to get mail using OE and love it's simplicity. I can reply, I can save to a different drive, etc so basically I do not need to fly a 747 Jumbo Jet to go 40 miles when a simple single engine plane (or car) would do. I don't get nuts onboard the single engine plane unless I buy them and bring them along. This is just an analogy. I don't need, nor necessarily want too much complication and bells and whistles just to read and reply (if I want) to email. I also use PoP Peeper email client to view and delete email on the servers since I have more than one email account and I can even reply using that email client. Cute little program, and gives great support even yet today. It is nice to delete all the feldercarb I get in email (read - JUNK) so I don't have to later on download it using OE6