The worst thing about all this for me is the truly atrocious attitude and complete ineptitude of AppleCare staff.
They have been a complete and utter failure. Their responses are full of the typical endless 'customer service placation language' they are clearly trained to say when they have zero actual facts to what is being asked. It's so bloody annoying!**
With this issue, they fail to understand any need for past OS download, and then have the gaul to question you in depth about why YOU need it, rather than go and find out what's going on, and then file an INTERNAL report about the issue. (It's none of their god damn business why I need it, I don't need to explain myself to people who don't have a clue about MY use whatsoever!!)
If you do explain some reasons (VM's, debugging, failure of current OS, etc.), they still completely ignore your concerns, and try and persuade you that High Sierra should be used, regardless of you explaining your software cannot use it yet. Or they say the TimeMachine/Recovery methods, despite you saying they aren't going to work.
The worst thing though, is how they also continually palm you off between staff members ("Store" people send you to "Tech" people, and vice-versa, with NO ONE taking responsibility for the actual question being asked, by dealing with the issue INTERNALLY before then coming back to the customer with the answer! No, instead they expect YOU to continually contact each AC 'team' yourself, when you have absolutely no idea on which AC 'team' you should be speaking to, given WE don't frigging work for Apple; THEY do!).
And then they get snotty with you when you get upset with their compete failure to take your question further.
They also use the endless get-out excuse of "escalating to engineering" – which from past attempts with AppleCare, is simply a euphemism for "go away, and don't expect any future resolution to your problem".
After dealing with countless 'teams', so-called 'Senior Advisors' who sound like spoilt children and have no idea, or apparent 'tech' team staff who ignore that you've tried all the things they're suggesting (after you've just told them you have!), and then take you through them again.
Quite simply, Apple mgmt need to pull their head out their backsides, and realise that this form of support, is NOT the way it should be done.
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** 'placation language' like these dross examples from AppleCare staff over the last 48h...
"My name is Angela, I’m a Senior Advisor with the iTunes Store. Your case came across my desk, and I wanted to make sure we did everything we could to help."
– let me throw up already!
"I know that you would like this resolved so you can update your computer, and I will be happy to guide you to a resolution."
– just give the answer, not ^this filler wank!
"Thanks for contacting us. I understand that you’re having issues downloading your MacOS. I know how important it is to have this addressed. Let me look into this for you and provide you relevant information."
– re-explain my question to me: why? And no, don't have a 'look into this' now, you should have done that already, then come to me with the one sentence answer to my query.
"To set your expectations right, your request for help has reached the iTunes Store Customer Support Team. I'm able to address billing, account, download, and content questions related to the iTunes Store."
– erm, I know your name and department already, because, like all letters/emails; you've put them at the bottom of the email already! And obviously "to set your expectations right" = euphemism for you have nothing to tell me; but keep using such pointless language, I'm sure it works on some customers who don't think it sounds silly and stupid!
...and plenty more.