Apologies, I phrased that badly.

What I meant was that on my reading of the rules, changes for rerouting are covered within the "contract" which is the one that you entered into when you bought the ticket. So it is not technically a reissue: it is a change that is permitted under the original contract. NOTE though that the rules explicitly say that for tickets originating in Area 1 (Americas) then a routing change before departure IS a reissue.

If you need to do something that isn't allowed within the "contract" then you have to cancel and issue a new ticket - this would be under the rules pertaining at the time.

The problem is that to get the contract under the "old" rules you need to issue the ticket before they change. That means you set the "Not Valid After" date for the whole itinerary as 12 months from the date of the first flight, as ticketed.

As I understand it, as you make changes to the ticket before departure, the Not Valid After date changes at each rewriting of the ticket to be:
- the NVA date in the previous version of the ticket, or 12 months from the first flight in the new version of the ticket, whchever is earlier.
So care is needed with these changes that you don't pull the start date too far forward unless you are sure you won't want to move it back into the future.

Hmmm... I hope someone can phrase that a bit better for the FAQ