I think I understand what you are asking.....does this help:
When a deposit occurs it is has a certain trade power assigned to it. In II, it is somewhat of a mystery, in RCI it is given points (tpus). The more desired the deposit the more points.
If you are searching in II....yes, there are weeks out there that you may not see because you don't have the power to pull them. It could be resort based or it could be season based. Example: you may be able to see many weeks at a resort throughout the year, but not high demand weeks like Christmas/Years. This means you had enough power to pull the resort...but not quite enough to get the high demand week there. Also. it may be you only have the power to pull studios, even though there are larger units available. The kicker is, you really don't know what you are not seeing...if you can't see it. Keep an eye on the sightings board, compare what others can see to what you can see and that may help.
RCI: As mentioned is a bit more straight forward You get the TPU value....say, 35 and when you search you can see exactly what you need to get the resort. Maybe 15 or 55 TPUs.