What happens with the usage ranks AFTER a filter has got a HU?

The usage rank is to reward the author for the work on the filter made, and this helps to reach the wanted HU award that is given.

BUT what happens with all the usage ranks received AFTER the filter has got this HU award? ( as there is no more higher lever than "High")

Are all the usage ranks lost and does not count anymore?

Or it is used to keep the High level because if the filter is not used anymore could loose the "high" rank and go back to "average" or perhaps even "low"?

I wanted to suggest also if perhaps could be possible to have a even higher level than "high" for filters that are even more used after the HU award, although without giving any further award.

I mean if would be possible to have a "Very High" level for the filters that are used much after a HU award?

HU = High Usage

Thanks for the answer GMM, this is what I have thought that they were for keeping the level of usage rank, but was not sure about it.