I have been using Unigue since it was sold in square steel cans. The last can I bought was 1 year ago. Been using the same loads of Unique in both 9mm & 357 mag for many years. Unique is probably my all time favorite powder.
As far as accuracy, I have not noticed any difference between old & new.
Alliant says the newer stuff burns cleaner. If it does burn cleaner, I have not noticed any difference.