This article documents a known issue related to the modified dates of Web Content versions.
Expiring a Web Content when System Setting Expire All Article Versions Enabled is checked, will update the modified dates of all Web Content versions to the current time.
STATUS: Won't Fix / No Solution Available
This issue will not be fixed since Web Content modified dates will reflect any effective change that affects Web Content data, metadata or status indistinctly.
There is a related Feature Request that you can vote on and follow: LPS-88514
Related Ticket: LPS-88564