Constricted air pathways
Be aware that a common fault with (especially) older accordions is that the coupler mechanism can often fail to fully open open the apertures to the reed block. (This may be caused by a twisted/or forced mechanism). The (barely noticable) consequence of this may be that the airflow to the reed may be slightly constricted, causing many of the reeds to sound slightly flat when in fact they are tuned correctly. In this case, it’s obviously far better to repair the mechanism rather than tune all the reeds to compensate.
High tech filing
Whilst using files might seem low-tech in this this day and age, it’s also possible to use a Dremel with a plastic polish tool to tune a reed (at least for the facing reeds), but whilst it is very convenient and creates a lovely finish on the reeds, a lot of dust will be created which may ruin the valves.
