Last modified: 2014-06-19 11:55:56 UTC
The log_search table began to be populated with protection-related information in Gerrit change #105443. Older protection events (prior to deploy of 1.23wmf15) lack the required log_search records, meaning Special:ProtectedPages is full of "unknown" timestamps etc. on big wikis like enwiki. It should be possible to write a maintenance script to back-populate log_search with the relevant protection data. Requires matching up log entries with records in page_restrictions.
Look at the last page to have it all filled ;-) https://en.wikipedia.org/w/index.php?title=Special:ProtectedPages&dir=prev I am not sure, if it is possible to always find the correct or related log entry. Page moves and reprotection can cause a problem here. On dewiki we also have protected pages without a log entry (see bug 24511), because the logging system does not exists at that point. So you would still have unknown rows on enwiki.