According to Reynolds some wartime manufacture No.4 rifles were found to require re sighting in after delivery due to shifts in bedding after being sighted in at the factory. A .01 gap was left between rear of fore end and face of butt socket on the theory that no contact there was preferable to unequal contact. They tried the same on the No.5.
Could be that in the tropics there was more swelling of the wood than a .01 gap could compensate for.
I believe everyone accepts that wandering zero is unlikely to appear in any No.5 rifles still extant.
Those rifles that exhibited the problem to any noticable degree were repaired or scrapped.
The vast majority of No.5 rifles in hands of civilian owners aren't likely to be abused to the extent that a combat rifle would be.