Yeah, as posted above it's definetly not the first or particularly rare. There's plenty of systems with two BHs in alongside neutron stars, white dwarf stars and other high mass stars. That being said, it's still a cool thing to come across! If you search in the system map for ''aa-a h'' or ''aa-a g'' (so for the sector these were found in search for Umbaiss AA-A H or Umbaiss AA-A G to cycle through such systems) you'll find a lot of systems with two, three or even more black holes in as well as neutron stars, white dwarfs etc.