1st set wore evenly, however the 2nd set was a bit of a mix.. Drivers wore evenly whilst Passenger wore on shoulders.. (Always check air pressure & was aligned twice)
Sorry to keep asking questions but was the wear on both the inside and outside shoulder. I know you said "Shoulders" - plural, but that can only happen if the pressure is low.
If just the inside, it's alignment (most likely camber). If it's on the outside only, then possibly camber but more often caused by using lots of roundabouts. No idea why it would only happen with the second set though. Except that points more to an alignment issue unless you moved from the country to the city and started using more roundabouts.
When you replace them this time, run 36 psi in the front (or 38 preferably.