Happy to report that my fix for iOS 9 click noises on the older apps is working great on my test devices.
I have submitted updates to Apple for:
ConcertinaXL (iPad and iPhone)
Hohner B/C Button Accordion (iPad)
The fixes for iOS 9 also improve the sound and stability for iOS 7 and iOS 8, so this is all good.
Assuming all goes well with the review process, once these are approved I’ll be using the same design to update the rest of the Hohner diatonic accordion apps.