Google will work out that the accounts are operated by the same person and forcibly link them together. They may then decide that you are abusively trying to evade their restrictions and permanently ban all of your accounts.
My accounts were created separately in the early days of YouTube and they got linked against my will. It doesn’t show up as my gmail account in YouTube because I kept rejecting their “please merge” requests, but besides the display name, they’re essentially merged and I have to log in with my gmail account. I don’t use my gmail for anything else anymore so I don’t care, but it was frustrating back when it happened. I know it’s just anecdotal and not a proper reference like you requested..
Oh, but you're talking about a pre-Google YouTube account being merged with a Google account, not two Google accounts being linked, right? Those are pretty different things.
There was a post on here (HN) a while ago about an entire company account getting suspended because Google had linked an employee of that company to his personal google account which was being used to re-sign Android apps for redistribution.
It’s an extreme example, but if that account is true, google definitely have automated tooling to link distinct accounts.
I can’t actually imagine any reason why they wouldn’t. It feels like something they’d need at their scale.
I actually have a few gmail accounts that are "Youtube banned" for same content ID thing but the mail/drive/whatever part of it still works.
So the "Google account wide" ban seems pretty rare and more motivated than just 3 copyright strikes.
