I'm using Strobe Tuner for Mac OS X to measure the notes, having convinced myself that it is probably accurate enough for my purposes. Ambient temperature is currently about 15C. I used the tuning software to measure the accuracy of each reed relative to A440, equal temperament.
Here, have the results as a pretty graph:
A couple of notes (no pun intended): 1. 100 cents is a semitone and the buttons are a semitone apart (apart from a few that are duplicated on both sides for convenience), so the worst reeds are nearly half way to the next button up. 2. because it's an English concertina, the reeds are in matched pairs; one plays when pushing the bellows closed and the other plays when you are pulling them open. They are actually mostly still fairly close to each other. 3. In theory, the D# buttons should match the nearest Eb buttons, as should the G# and Ab buttons. They don't. Not even close. They make quite an 'interesting' sound when you play both buttons together! 4. Nearly all the reeds are significantly sharp. I suspect this is mostly due to the steel tongues work-hardening over the years, though it's quite possible the instrument was originally tuned higher than A440. I don't know why a few of them are flat instead.
 I think it's accurate to a fraction of a cent, checked by using it to measure a 440Hz reference sound file played on various different devices.
 I know the temperature makes a difference but I'm unsure how much or how to compensate for it, short of heating the building to 20C which is easier said than done here at the moment.
 This is the modern standard most commonly used to define the frequency of each note. It didn't exist when my concertina was made. I don't know what temperament or reference pitch it was originally tuned to, and it's clearly drifted out of tune anyway so I might as well work on the basis that it will eventually be re-tuned to the modern standard.
Other things done on the concertina since the last update:
* I laminated the rosewood veneers together to make the boards for the new ends. They have been drying in a press for over a week now. I'll probably write a separate post about them later once I think they are fully dry.
* I cleaned and polished the bellows with the Meltonian neutral shoe cream (took about an hour). They came up very nicely and still look to be in fantastic condition for their age.
* I've been continuing to drive myself and everybody else crazy by practicing the Winster Gallop for a few minutes several times a day. I think I've mostly got the hang of it now, though I'm trying to get to a stage where I can consistently play it at a decent speed without making more than the occasional mistake.