An X509 certificate revocation list contains a field specify

An X.509 certificate revocation list contains a field specifying when the next such list is expected to be issued. Why is that field present?

Solution

Next Update Field in X.509 CRL

This field indicates the issue date by which the next CRL will be issued. As mentioned in RFC 5280, the next CRL could be issued before the indicated date, but it will not be given any later than the mentioned date.

When displaying next update field is selected in the CRL tree and is displayed on the panel in the right side, the date held by it is verified against the current date, and if the date is exceeded, a alert red notice with message will be displayed under the field as a reminder that maybe a newer CRL has been issued;

Simply

There are two distinct semantics that the nextUpdate field is used to convey: