When you secure the valve nut does it mechanically stop or does it pull core up tighter against seal?
If tighter then seal would be damaged over time if nut closed overly thight (which is what I do). Reason I ask is because about 1,000 miles ago I installed a tube with stem to short for presta air chuck. I had to use schrader adapter which I decided to leave on with nut loose enough to add air. One month later new tube needs air weekly and the other almost daily. Newer tube uses only air pressure to seal and is holding air better than any tube I can remember.