How to reset guest users counter?

Hi

I've noticed that every time I create batch guest users, the number in the username keeps increasing:

user0250

user0251

user0252

...and so on.

I have already deleted all users and the guest group.

However, after creating a new guest group and generating new batch users, the numbering continues from the last user (e.g., user0253, user0254...).

I can't find where this counter is stored or how to reset it.

Thanks.