There’s only 2 places left to look, in the neck pocket and under the truss rod cover!
If you’ve never taken the neck off of a bolt on bass before it’s relatively easy to do, just loosen the strings until they are completely slack so there’s no force pulling on the neck and body, then you can unscrew the neck, just make sure they are all the way out before you scoot the neck out of the pocket. You can leave the strings on, just gently push down on the neck and slide it back, so you’re not putting any unwanted force on the edges of the neck pocket. It should slide up and reveal the neck pocket and the base of the neck. There should be at least some sort of identifiers in there.
The truss rod cover probably doesn’t have anything but the truss rod hole under it, but it could at least show what kind of nut is on it. Which someone might be able to figure out
If you’ve never taken the neck off of a bolt on bass before it’s relatively easy to do, just loosen the strings until they are completely slack so there’s no force pulling on the neck and body, then you can unscrew the neck, just make sure they are all the way out before you scoot the neck out of the pocket. You can leave the strings on, just gently push down on the neck and slide it back, so you’re not putting any unwanted force on the edges of the neck pocket. It should slide up and reveal the neck pocket and the base of the neck. There should be at least some sort of identifiers in there.
The truss rod cover probably doesn’t have anything but the truss rod hole under it, but it could at least show what kind of nut is on it. Which someone might be able to figure out