Historically, accordions have always been tuned a little sharp. There may be some historical reason for this. But if you intend to play with other instruments which you know are tuned to 440hz, I see little sense in tuning an accordion to anything else. So the bassoon reed (16′), piccolo(4′) and clarinet(8′) reed should all be tuned to 440Hz.
Warning! The upper piccolo reeds are incredibly difficult to tune due their miniature size. I would, certainly to begin with, for non-facing reeds, heartily recommend removing the reed plate for every operation, so that all reeds may be filed from above.
For the tremolo (8′), may I recommend the lower octave to be tuned to 441.5Hz, and the upper octave to 440.5Hz. And 441Hz in the middle.
So why not tune the whole tremolo register to, say, 441Hz?
Frequency is exponential. So if A is 220Hz, the octave higher is 440Hz and the next octave is 880Hz. Numbers get pretty big, pretty fast. As a matter of fact, accordions (and other 12 tone instruments) are generally tuned to the ‘tempered’ scale – which means that many of the notes are just approximations of their respective natural harmonic. So there is an inherent ‘error’ i.e. the difference between the tempered pitch, and what would be the natural pitch. So as the pitch increases exponentially, therefore so does the perceivable ‘error’!
The principle of the tremolo artificially creates a second ‘error’ in order to mask the inherent ‘error’ of the tempered scale. However, in the upper octaves, the ‘error’ of the tremolo may actually become uncomfortable to listen to if not deliberately curbed.
Hence the tremolo at the top should be less that the tremolo at the bottom.
Inversely, a wide tremolo at the bottom does tend to sound very pleasing indeed.
Edward Jay's Accordion Know-How 