Per the HPD Open Standard Version 2.0
A new HPD may be published or an updated HPD republished using an outdated format for up to one year after the next major version of the Standard has been released (2.0, 3.0, 4.0, etc.). However any HPD using an outdated format expires three years after the next major version of the Standard has been released (e.g., an HPD using Version 1.0 expires three years after the release of Version 2.0).
For reference purposes, the HPD Open Standard Version 2.0 was released in September 2015 and the final date to create or update an HPD in the Version 1.0 Format was September 30, 2016.
All completed HPDs using the Version 1.0 Format will expire on the earlier of their Expiry Date, or September 30, 2018.