I measured my 2012s prior to selling them recently and they were 14hh (dams are all between 16hh-16.2hh. Sire 17.1hh). I only have two 2011s here now and one is 16hh (dam 16.1hh, sire 17hh) and the other 13.2hh (dam 15.2hh, sire 17hh). The 2010 I have is 15.3hh (dam 16hh, sire 16hh).
My yearling and 9 monther have always been the same height even when the younger one was newborn (massive shock when she stood up). I haven't got a stick to them but they are the same as my 2 year old and I reckon 14.0 - 14.2. However the big filly is a Clover Hill mare x Ricardo Z and they typically can get to 17.2 - 18.0 so no surprises really. Both mares/stallions 16.2 ish.
However, I have found that things do 'even up' to an extent between birth and 6 and that all of these size rules don't really work tbh. Perhaps they do with natives etc for what they were invented but not once you start mixing blood.