The AI never retrains, from what I understand, so if you just don't retrain, it shouldn't be a problem.
The AI occassionally retrains, but its rare in 1.2. After 40-50 years you'll start to see triple silver and quite a few golds at full strength coming out of very heavily fought over area's. As an example in my Romani campaign (VH/VH) the audeui now have a couple triple gold chevron gestatea its 211 B.C. Lot of it has to do with the difficulty of the campaign map, and I believe the harder battles may help too since all ai to ai battles are auto resolved.