No records have been sealed, so there is nothing to verify.
It proves nothing has been changed. Each record is hashed together with the hash of the record before it, so altering one would break every link after it. That is what this page checks, from scratch, on every load.
It does not, by itself, prove a date. The seal is produced by this site, and a date is only worth something when someone else recorded it. That is what the GitHub merge record on each build entry is for: those timestamps come from GitHub, not from me. The chain head above is published so it can be checked against an outside copy.
Saying that plainly matters more than sounding airtight. Anyone can check both halves.