So I seem to have figured it out. Even though ADE was requesting some sort of unknowable Vendor ID what it apparently was asking for was a different User ID. The books in question were purchased under a different account and so, even though ADE authorized my computer for the account I normally used, these particular books wanted a different authorization. Digging way way back into my email and finding another account was the only way I was able to solve the issue.
Incidentally, contacting Adobe directly did not work. Doing a google search was useless (except to find others in the same boat as me). Trying to read the docs... well that's a laugh.
The entire process has left an incredibly sour taste in my mouth. I normally stick to paper books for this reason and I am going to continue to do so from here on. When I DO purchase e-books I will do so with the following priorities:
1) Never buy books that use Adobe DRM. Kobo has a single point of failure. Amazon is the same way. Adobe... well since they sort of graft their tech onto other stuff it just turns out to be a giant clustertruck. I hate DRM for the reasons mentioned in my above post, but I have never ever ever had to deal with a DRM scheme as badly executed as this. Multiple accounts for a single asset (Sony account + Adobe account)? NO technical support whatsoever? When you run into trouble you have to try to figure out what incoherent and incorrect error messages are trying to say about business structures (vendor id? wth?) that make absolutely no sense to the end user (I bought books from the Sony store which was then purchased by Kobo - why the hell am I debugging Adobe software and Adobe accounts). ADE seems to require a level of technical proficiency comparable to software of the early 90's. The whole industry has moved past this point. ADE has not.
2) When buying books, try to avoid DRM altogether... but when you cannot do that make sure you get some that are able to be liberated from that jail. Not going to mention how to do it here, but I understand it is possible to strip the DRM from these books. If I were to do that, I could then be assured that I could continue to read the books I purchased no matter who goes out of business (Sony books, I'm looking at you) or what device I decide to upgrade to or how lousy the DRM technology is. Were I to go down that route, then I would still always purchase my books, but immediately convert them to a format that will never ever give me technical troubles again (AND let me save my annotations in an unencrypted form).
Sorry for the rant, but this (plus the Sony to Kobo transitions) has been one of the WORST digital media experiences I have ever had.
I completely agree. The customer support is beyond worthless. I don't have the original ID I used and the advice from customer service was to check with other users of the forum. I have never experienced anything so pathetic. I'll never use ADE again.