Bernard:"It is standard practice when tuning an accordion (and other free reed instruments), to make the lower pitched bass reeds a few cents sharp so that they blow into tune"

RE: I can't quite agree.You don't "make them a few cents sharp" since the point is that the pitch stability vs amplitude is gradually less for lower range reeds and the aberration in the low octave of a treble english may be 5-10 cent while in a baritone up to say 20cent so you usually decide a common testing air pressure for the instrument and set the pitch straight according to that but you may of course decide the balanced pressure/amplitude differently and to some part according to the expected individual use.
Because of this any free reed instrument can only be "in tune" at one specific pressure/amplitude - a certain disadvantage but fortunately we often don't bother a lot subjectively when they are out of tune...