Ok, I have done some research on all the background files, so now let's make it clear once for all :
There are 20 BLACKBGx.DAT files.
--> Numbers A, F, G don't contain dialogs nor events (it's obvious when you see the size of those files : 2 ko).
Among all the others files :
--> Numbers 1, 9, C, E, J are not related with the debug room.
--> Numbers H and I perhaps contains commands for the debug room at the end of the script, but I am not sure.
--> All the others (2, 3, 4, 5, 6, 7, 8, B, D, K) contain events of the debug room.
Note : Numbers 1, 6, 8, C, D can now be opened by Hack7.