Hmm.. :-\...often after drastic 'treatment' like moving mature plants from one place to other will result them starting to 'sulk'. That can take several years and after that they are ok..sometimes they will never get back to their fomer glory.
The older they are when you transplant..longer they will take to replace all the roots that where keeping all the growth going on and they have to produce more roots for the new growth as well. So yes..it is quite possible 2 yrs is still 'early days'.
There is not much at this stage that you can do other than give them annual dressing of bonemeal..to encourage/aid the formation of the new roots..making sure they don't struggle with lack of moisture would help too.
Application of all round feed like BFB or even bit of chicken pellets won't hurt..perharps your grapes need bit of 'fattening up' to get them kick start. Generally I don't feed grape much..but when they struggle, little pampering don't hurt.. ;)
If they do some top growth..don't let it 'go' far..but keep it trimmed quite short for now..they will otherwise waste their energy for all the new growth when they need to grow good, strong root system.
That's about all I can think of at the moment..hmmm...mulching is good too.
