When trying to calculate TPU value at a resort, I use the Deposit Calculator to test the present value of a given deposit week. Working through the calculator calendar with the same deposit will show a range of what that week is worth. That gives me the range of which reservation week to request from the resort if I intend to deposit it with RCI. (Other companies may not be so strict, which is why I've grown to prefer SFX over RCI.)
In my experience, weeks in July, specifically around the July 4th holiday, tend to have a higher value than the same deposited unit in June or August, and even later in July. After Labor Day the value may drop again. Things tend to follow the holiday calendar, with holiday weeks generally having a higher TPU. It varies by resort, of course, and the relative desirability of what is being deposited.
So the best test would be to find the value this year of the exact week and unit you deposited last year. If there is a great value difference, then there is reason to question whether the resort has lost value in RCI's estimation.
Dave