Recycle previously used user numbers?

WordPress automatically assigns the next sequentially available user number to the next user added.

However, previously added users may disappear for any number of reasons, most often because a user account was created but never used. One may then end up with Current User 121, Current User 122, Former/Gone User 123, Current User 124, Former/Gone User 125, Current User 126, etc.

In order to conserve the number of user numbers actually used, in the example above would there be a way to override WP automatically making the next user 127 and instead force it to re-use number 123? This would of course be assuming there is no content associated with 123 any more.

If there really is no upper limit to the user numbers, this may be entirely unnecessary, but I am under the impression the software stops adding users after number 999.

Any thoughts appreciated.