A I understand it, 'Model Years' run from September to August, and are giving the number of the following year, so:
MY13 = Sept 2012 - August 2013
MY14 = Sept 2013 - August 2014
MY15 = Sept 2014 - August 2015
If there's a need for a spec change mid-model-year, I believe it gets a '.2' or '/2' suffix (eg 'MY13/2')
These dates should refer to when a car is built, so cars from (about) build week 36 (Sept 2nd-8th this year) would be MY14. This does mean that some second-half-of-year ('63' this year) registered cars will by MY13 due to being built before the factory shutdown.
Hope that clears up some of the confusion.
Mmm sorry about the earlier typo. More haste less speed required
MY 14 is what we are going to buy from September 2013 to July 2014 if the car was built from September 2013 onwards.
I agree that it all depends when the car was built.