Note that there are two different types of crew experience - crew quality (I forget the exact name) and task force training. I'm pretty sure that Erik was talking about the task force training one, which is acquired by putting a TG into "train" mode.
I suspect you might be talking about crew quality, which is determined by your academy level and the captains crew training bonus. Basically, your pool of available crew members all are of the same quality (determined by the academy level). When a crew is disbanded, then the total quality of the available crew pool expands by the number of points in the disbanded crew. Since such a crew will normally have been "trained up" above the pool's level, this means that you'll insert more crew members (of lower quality) than are in the disbanded crew into the pool (this is a simplification to avoid having to track and manage different quality crew members in the pool).
Whenever you move the training level up, you cut the number of crew available in the pool in half, so temporarily bumping up is a bad idea.
John