It doesn't seem like the map updates correctly for bases destroyed by the fire blast wave. Guessing limitation in Factorio that you may need to trigger the update on the affected entities somehow?
https://youtu.be/fQ9vWs5dKpM?t=1496

That is because the "radar" component is in the fired shell, once it hits the ground, you no longer get updates.
The only way to fix this is probably to kill everything right in the moment of impact instead of in an cascading explosion.
Indeed it seems someone tried exactly that in a fork of this mod: https://github.com/helpfuljohn/AtomicArtillery/commit/0c677cd939b8a7d32b927aa7bea91381f39066c4

Yeah, it's a shame that the options are either having it look cool or having it update the map. I prefer it looks cool, perhaps there might be a way to actually force a map update for that area but I'm not much a of a modder so if anyone figures that out they're welcome to give me a shout.

You can have the artillery shell detonation trigger scripts, including charting. I'm not sure how to obtain the proper force for charting (to handle all cases such as PvP), and it might need a delay (though charting creates a certain time of visibility, it might not last long enough in every case).

https://lua-api.factorio.com/latest/events.html#on_trigger_created_entity
https://lua-api.factorio.com/latest/LuaForce.html#LuaForce.chart

Similar logic here: https://github.com/justarandomgeek/factorio-botshots/blob/master/control.lua

sadly it use to work correctly in .16 it would show you the whole explosion even if it didn't update the fog of war correctly

it's finally fixed, no thanks to me because I haven't got a clue what I'm doing to be honest.

https://github.com/sirdoombox/AtomicArtillery/pull/3