Well, I think it is obvious that they mean the start date.
They can not, for example, call you an tell you:
"you will start in 2015 but hey! we called you before the 12 months were gone so it is fine".
Regarding the extension of the 12 months.
It is just a feeling that I have but Emirates guys seems to be quite "professional" or "strict" on that kind of things. If they say that something works like that I don't expect them to be making exemptions. Some of us will have to re-assess again but well, we did it good once I guess we can do it ok next time!