I've had a mix- I've had two newer set necks with adjustment capability, and two older with no adjustment. The two older models didn't move much within the string gauge ranges I use (0.30-.118 to .045-.130), but the newer ones will a slight bit. Luckily the older models were static with light strings at a straight neck, and would move to very gradual relief with heavy gauges. I would not posit any confident hypothesis for why older vs. newer necks move differently, because the n is small and there are a lot of variables- minor changes in internal neck structure to accomodate adjusment rods, age, etc.
If I HAD to guess though, I would say with age and seasoning, the older necks settle into their 'equilibrium', and the stiffness of the carbon necks requires a large tension delta to get much change (relief or backbow). The newer necks move a bit more because they haven't hit their relaxed state with age. Carbon composite definitely settles over time in various ways, so it isn't surprising.
I've never owned one that was out of whack or screwy or that moved like a wooden neck with string gauge changes, but of course there is potential for getting a neck that is on the edge of relief with a particular gauge that will move into unacceptable with thicker strings.
It varies bass to bass. I'm really picky about it and I need a dead-straight, no-relief neck, so I would probably want to play an old set-neck bass before I purchased it, but most people would have no issue. I've seen that they generally settle into having a bit of relief, which for most people is ideal.
If I HAD to guess though, I would say with age and seasoning, the older necks settle into their 'equilibrium', and the stiffness of the carbon necks requires a large tension delta to get much change (relief or backbow). The newer necks move a bit more because they haven't hit their relaxed state with age. Carbon composite definitely settles over time in various ways, so it isn't surprising.
I've never owned one that was out of whack or screwy or that moved like a wooden neck with string gauge changes, but of course there is potential for getting a neck that is on the edge of relief with a particular gauge that will move into unacceptable with thicker strings.
It varies bass to bass. I'm really picky about it and I need a dead-straight, no-relief neck, so I would probably want to play an old set-neck bass before I purchased it, but most people would have no issue. I've seen that they generally settle into having a bit of relief, which for most people is ideal.