Tilting at windmills maybe, but I think all manufacturers should fix at their cost any rifle that has drifted over the limit, at any time in its life and this should not be a time-limited warranty.
After all, when you bought the rifle you asked for a sub 12 fpe rifle. If it's gone over through no fault of yours then it's not fit for purpose.
Once it was no longer a money spinner we might see a different and more sensible approach from the manufacturers. As it is now, they almost have a vested interest in your gun creeping up.