Okay somebody get to the bottom of this.
Somebody lay their bass flat without the headstock or any part of the neck touching the surface it's laying on and tune the bass.
Then take the bass and put it on standing up as if you were going to play, and check the tuning.
Did the strings go tad flat ? If not you probably got a good stable neck. If they did go a bit flat, not so much.
I would check myself but I don't care
Somebody lay their bass flat without the headstock or any part of the neck touching the surface it's laying on and tune the bass.
Then take the bass and put it on standing up as if you were going to play, and check the tuning.
Did the strings go tad flat ? If not you probably got a good stable neck. If they did go a bit flat, not so much.
I would check myself but I don't care