Surely there would have to be some sort of pre-issue trial at squadron strength or smaller, prior to general issue?

Maybe that would cover these little inexplicable situations..

Quite correct and it is surprising just what a large scale some items are issued on for pre acceptance trials. Thigs like new types of clothing are trialed at Regiment and sometimes Brigade issue scales. The harder use it is likely to get the larger number of people it is issued to purely to find out how durable it is under various conditions of use.