I don't quite understand the question regarding Armourers replacing the wood Big Stick. But if you mean after stripping it down to do a repair or something such like, then they'd ALWAYS replace it with the same wood. That is part of its accuracy (or lack of it in the case of a hot No5.....!). But if it was to be replaced because it was loose or battered and bruised, then we didn't care who made it. We'd just fit it properly, re-number it to suit and send it out. But generally speaking, those No5's that had seen a lot of service could have very loose fore-ends longitudinally. We'd refit a replacement that might possibly be a used one from another rifle, patched up, deep linseed treated and sent out again. The heat, stifling humidity and rain plus the salt water silt were very unforgiving to No4 and 5 woodwork and it's suprising that some lasted more than a few years.

Anyway, when we got a batch of re-useable fore-ends we'd have a bit of a run and patch them up with new draws etc dry them out, bath them in linseed and leave them on the shelf for the next batch of needy rifles. Another thing that would make a fore-end scrap was the top sling band because while the leading scouts used shotguns, those following had machettes and had the rifle slung so it was always pulling against the sling band that would chomp its way into the contracting and expanding wood. And if salt water got under the fore-end cap, then forget it. It would start to rust within about 10 minutes so off they came. The holes would be glued and plugged and the fore-end made off to shape.
Anyway, does that sort of answer the question, even if I didn't quite fully understand it?