You’re correct but you’re also missing the point. If law enforcement outright says that they won’t show up to enforce a law, there isn’t a difference between following that law and breaking it. You face the same consequences.

Effectively, yes. Going ten over the limit here isn't "legal", per se, but it's not something you'll be pulled over for, so everyone does it. It's "legal".

Plenty of people get pulled over for going ten over, some states are known for pulling over for anything over the limit. Hell, lots of people get profiled and pulled over for nothing at all. It’s so interesting to see this kind of privilege on display, thinking that pushing the legal boundaries is now technically “legal”.

Still illegal, but police don’t prioritise enforcement. This can be written precisely.

Eh, de facto legalised. When states legalise marijuana and the Fed’s don’t enforce, we freely call it legalised, even if that isn’t technically correct, because it practically is. Shoplifting is de facto legalised in San Francisco.