Which single entity can be trusted? None beyond the US federal government exists today, and they don't want to do the job.

I suppose in theory all of the industry players could get together and establish a joint venture or nonprofit company specifically for the purpose of creating and maintaining an accurate database of provider contact information. But that seems a lot more complex.

Doesn't seem that complex to me. Insurance companies kinda do that already. It's not a technology issue, otherwise Google or Microsoft would have figured it out already, it's a governance and legal issue. Blockchain doesn't seem to be bringing to the table anything valuable in this case.