Agreed! Why is it happening on both Mavics and not the Araya? (haven’t swapped the rim tape).
So this afternoon I up-ended the Hardrock, removed the tyre from the Araya, and compared the valve holes.
1) the Mavics have a box section construction, thin metal is used and the strength is obtained from the box section.
2) the Araya is not box section, so the strength comes from using a much thicker alloy.
The tyres seem to slide a bit on the rim, over a period of time. You can tell this with Schraders since the valve stem sometimes ends up at an angle to the rim (instead of being vertical).
So perhaps, occasionally, the thinner metal digs into the side of the valve stem?
I don’t know, it’s just a theory … I haven’t had a puncture on the Araya rim in around 15 years!
(which now means I’m heading for one!)