Which is why an
independent SME is often of benefit. Someone familiar with the requirement and who has also advised the COTS supplier of the aircrew needs.
Independent testing will reveal whether the COTS supplier has fully understood the system requirement (assuming it had been correctly specified...
) - then bench/flight testing with the end user to assess whether the end user is being picky about a new requirement which his specification writer forgot about or is using the system without having RTFM or bothered with any training etc. The independent SME assessor will be able to arbitrate fairly between both sides and recommend whether or not , in his opinion, the kit meets the specified needs of the user.
Relying upon a supplier to simply read the spec. and nail the system into the aircraft
without any independent assessment will often lead to tears!