It got downgraded to B (maybe even C) class at some point because it was in a dire state. Over the years I (and others) have spent quite some energy into getting it to its present state. (Hence I much appreciate your compliment.) I currently don't have the time or energy to get it to FA state. However, if someone were to make the effort, I'd be glad to help out. I think to get there, it will need some minor updating for developments over the last 5 years or so. In particular, it should probably mention ongoing efforts of the Event Horizon telescope and GRAVITY to provide more direct observational evidence for the existence of a horizon.   