People greatly underestimate just how important the Technical Data Package is for a firearm. The specifications and, critically, the tolerances can make or break a gun. Not having the tolerances for measurements means that sometimes you literally cannot recreate something.
(This is why you see so few recreations of certain guns despite a forgery being worth hundreds of thousands of dollars despite being a couple hundred dollars in materials and labour, amongst other things.)
Improper tolerances can also cost lives in war. During WW1, the Canadian Expeditionary Forces were issued two types of .303 British ammo, one from the Canadian supplier, one from a British one. The CEF’s Ross Rifles were spec’d and toleranced for the Canadian Ammo. The British Ammo jammed and failed in the Ross Rifles but not the British Lee-Enfields. The Lee-Enfield was designed to handle much greater off-spec and out-of-tolerance ammo.
The Canadian supplier made the ammo to the specs and tolerances that .303 British round specified in the TDP. The British supplier didn’t. The Canadian supplier made bullets for a living. The British supplier made cars, I think.