Camera setup and use can be a fussy process, but there’s nothing dynamic happening under the hood - after your initial lens calibration and overlay alignment, the numbers will never change unless you overwrite them with a new calibration or alignment.
What can and sometimes does change is the relative position of your camera to your workspace - if the camera is loose on its mounting location, mounted to a lid with some play in its hinges, or not always returning to the exact same position as it was when you first ran the alignment, that can cause misalignment. If you have a tabletop engraver and it moves, that can cause misalignment.
If you switch to a thicker or thinner material and do not have an adjustable height bed, that can cause a misalignment (the height between camera and workspace will have effectively changed).
The calibration process with the dot pattern can be tricky, but that is generally a one time only process. As long as you achieve a good result with that once, you should never have to do it again, regardless of the position of the camera. This may be related to the conflicting advise you’ve seen - the calibration process does not need to be done with the camera mounted, only the alignment step doesn’t.
Support for head-mounted/gantry mounted cameras is relatively new, still in a beta-ish phase, and not yet documented. In time we’ll have resources available on that subject.
For now, here are some resources on the overhead camera alignment process:
