Prior to the related change, clients may have written down X-Delete-At headers
that are outside of the Timestamp range, for example.
Change-Id: Ib8ae7ebcbdb32e0aa58446bd1ef949e5e2f63e74
Related-Change: I23666ec8a067d829eaf9bfe54bd086c320b3429e
Related-Bug: 1821204
Partial-Bug: 1860149