The phrase at the time was Make Do And Mend. I would think that the original flaw in the stock was perhaps discovered at final inspection, It was certainly standard practice at the motorcycle factories of the time like BSA and Triumph for any defective bikes or engines to be put to one side and any replacement parts needed ordered from stores. Their faults would then be fixed either by repair or replacement at weekends, so as not to hold up the production line during the week.