A fan, in the working sense, is a listener who has left a way to be reached. Not a follower count and not an audience figure: a person who asked to hear about the next thing.
Why the distinction matters
Platform followers belong to the platform. They can be reached only when the platform decides to show a post, and they do not travel when an artist moves. A list of people who asked directly is the one audience an artist keeps.
What it obliges
Somebody who asked for one release did not ask for everything. Every mail after that has to be the thing they asked for, and every mail has to carry the way out. The moment somebody asks is the consent, and it stays attached to what they asked for.
Counting them, not naming them
An artist wants to know how many people are waiting on a release. Nobody needs a list of names to make that decision, and holding one turns a number into a data protection problem. The count is the useful part.