Hello! This is just a curiosity question. Can a professional ear hear when playing an instrument (in this case an euphonium) feel and hear that the (perfectly tuned and perfect valve movement etc) instrument has been left unplayed for many years even if the instrument has had a sufficient warm up of 30 mins? I would guess that once the brass is warm it would have the same sound as a regularly played euphonium but maybe there is more to it than that?!!