First, thank you to the lovely club members that were able to guide our friend through this pickup screw situation. Glad this was easily remedied. And while shipping (another source of vibration) can wiggle those screws into wonky positions, once your upper pickup screws started to loosen, the weight of the pickup in a playing position can coax them out further. They can wiggle up or down since they are machine screws.
One thing I can't imagine is what could support a pickup for four years if the lower screws were bottomed out from the start.
An important point here: pickup height can make a difference not only in playability but also in tone. The hard thing is that it's difficult to discuss the difference in tone because it really changes depending on how you play and what strings you like. It's one of those things that you really have to drive there yourself to see if you need it different from the default. Also not everyone is sensitive to these changes, but most Alembic players are.
Another very important point here: we do great set ups, but they may not be your favorite setup. For instance, there is not a standard for the pickup heights or even string heights. We set up the bass impossibly low, then raise the action a bit, than we know it can go lower, but it will be easier to play for most players, and especially for those who have never played an Alembic. The pickup height is normally bass pickup on the low side, treble on the high side, but there is no fixed measurement here. In fact, we fully expect that every player will change the pickup heights, truss rod tension and the bridge height immediately or at some point it the future.
