Martin, I was sure that it was your name I saw on the credits
on the Carthy/Waterson CD I purchased from himself at Mystic
Seaport when he was with us a few years back.

The 'Club' system boxes are almost always C/F tuned with that
half-row of accidentals and a perverse two-way button (usually
in a contrasting color) on one of the rows. Quite a popular system
in Blighty up through the 1950's, it would appear, as there are
quite a lot of them about from that era, usually in various states
of disrepair.

In more recent years, with more and more custom boxes around,
partial third rows in custom tunings seem the rage; I honestly
have yet to see one that wasn't a better idea on paper than in
practice.

We shouldn't fail to mention the Continental Chromatic button
system, which is a fully chromatic accordion with what arguably
is a much more rational keyboard layout than the piano keyboard,
in light of the space limitations inherent in a 'stomach Steinway.'
The magic of that system is that it plays the same note in and
out, and using four or five rows of buttons can play in any key
using identical fingering just by starting on a different button.
They usually have a stradella bass, and weigh in the range of a
lighter piano-accordion.

Many people call the 3-row B/C/C# (or C/C#/D) instruments
with Stradella bass "Shand style" accordions in honor of the
Great Scot. It's as different from the fourths-tuned diatonic
boxes as chalk and cheese. It's a testament to John Kirkpatrick's
talent that he is a virtuoso on 1- 2- and 3-row diatonic boxes,
the 'Shand' system, AND on Anglo concertina. All while singing
talking and/or dancing at the same time.