In program BeerSmith there is a tool Hops Age, which can calculate loss of AA. Noble hops from 2007 harvest loose about 1% AA by now, quite a bit.
On the other hand Ray Daniels in his book says, we don't have to make any of such corrections, properly stored hops don't loose much bitternes, which comes not only from alpha-acids.
In practice, do you re-calulate the AA of aged hops or not?
How about aroma hops? Do you use more of them, when they are one year old?