I don't believe it, but I believe that they may not have been noticeable to you.
I also believe that if you did some controlled DI test recording or better yet some oscilloscope viewing, you'd be convinced.
Notes just blow up. The closer you scrutinize basses and their designs, the more amazed you become that they ever work
at all.
Nearly everything plays a part in it.
Bridge mass does quite a bit -- at least indirectly -- but not consistently. The more mass in a bridge, the more inertia, which retains more string vibration without passing it into the body through the bridge. This is the physical principle on which the high mass bridge concept works. The more string vibration you can retain and the more the string is isolated from the body, the less apparent the dead spot.
The problem with the GL you mention is probably mostly to do with a whippy, conventional neck and probably its poor seating relative to the pocket. If that's bad, it's going to be tough to hide a dead spot.
But there are so many things that contribute to dead spots because they are so vibrationally complex that it's hard to really tell exactly what the prime culprits are. Technique can even make a huge difference, and it's a good thing as there may be nothing else that's going to do much good.
Having a dense body, a well-seated graphite-reinforced neck, plinky roundwounds and a high-mass bridge will usually minimize and
mask a predictable dead spot to an untrained ear, but it's not the sound I'm after.
Yes, and to make it worse, they're not obvious. CLF was convinced he'd screwed up the headstock design by putting the G where it was, so placed it in the MM 3+1 location to reduce its apparent dead spots. I think it works to some extent.
Of course, when Fender basses had foam mutes under the bridge covers, none of this was as apparent anyway.