although I can't say I have one bass that holds tuning "unbelievably well" since I own a lot of them that I never have to mess with, but the one that always surprises me is my KahlerTrem'ed Jackson. I can dive and bend on the strings as much as I want, let go of the bar and I just laugh because it is always in tune, despite the wonky string angles thru the nut.
I don't see the relevance of people saying "my bass sat in the case for a year and when I took it out it was still in tune", because if it is just sitting there it should. It is when you are banging on the strings where most of the tuning issues occur, because if that was the case, I have a dozen collectibles that do nothing but look pretty and they are always in tune.