Originally Posted by Happy

I know the HHonor site would let you book beyond 12 months if you IGNORE the error message and proceed on 365 days beyond, the site let you.

As for the cert, look at your reservation confirmation - there is a Reward ID or something like that - that is your Cert Number. It is unique. For a fact, I knew of someone who initially booked within the 365 days window, then went back to CHANGE the date to Nov 2014 - the website let her, and the new confirmation has a new Reward ID. However I seriously doubt the new Reward ID (Cert) would give a Nov 2014 date. Well, in her case it is just Conrad Tokyo - if she is refused at check in, it is not too expensive to find another hotel, especially if you are willing to downgrade a lot, you could manage with about $100 to $150 a night. Not such case if you are at Maldives or Samui.