Pro 'Burn in' time.

[ogs]

(IMO) 100% of it would be measurable with the right kit, people, time, and carefully designed experiment. But pretty much none of us has acess to any of the required tools, generally we have our ears and the playback equipment.

Yes, with the right kit - which has not been invented yet! It should be possible to measure this as it can be quite a difference, but I do not think the equipment exists. Or it may exist, but the measurement methods does not reveal these differences.