I can totally believe that may exist too. After all, for the CDN / Hosting company, what's the real risk? It wouldn't shock me if lots of infrastructure lets

I can totally believe that may exist too. After all, for the CDN / Hosting company, what's the real risk? It wouldn't shock me if lots of infrastructure lets you board a new and novel host label that hasn't already been boarded and starts letting you configure things like a custom TLS certificate to be associated with that label. As long as they watch out for uniqueness, what's the risk to the CDN? That a config context gets created for a DNS label that isn't yet pointed there? It's not an obvious risk from the CDN's perspective. Even for an invalid domain. "Oh, sad, I just wasted mere kilobytes of storage on a configuration for a domain that you're never going to actually be able to get into the DNS and point to me?" That sounds kind of low cost, from the CDN's perspective.