I know some of our corporate rates are a set $.

So for instance it is always $150.
But the hotel may have rates as high as $300 during high season and $100 or less on off times (and weekends).

Others, the rate varies.
For instance I have yet to figure out the pattern for NY where there is sometimes a $200 difference week to week on corporate rate.

I have seen similar of AAA, where it will sometimes be more expensive the regular rate.