Well, Dick, a harmonica player has to use considerable breath pressure, which can slightly lower the pitch of the notes. Different players have different breath techniques; mine is a gentle huffing and puffing, which makes my instruments last a lot longer, and skilful use of that technique can project the sound just as well as hard playing (we're not that loud...)

I note that your explanation of piano tuning makes no reference to stretched octaves. I think you need to look that up. Additionally, I repeat my earlier assertion that you would never detect sharpness with a harmonica tuned to A441 (or even A442). They are universally tuned that way out of the box. I check the tuning of any harmonica I buy, and I adjust them to A441 or 442 routinely, if they need it.

Do you know the fine-tuning of your concertinas, Dick? Do you check them? Can you tweak them yourself? Many years ago I bought a Hohner Erica D/G button box. The thing is tuned way higher than A442. It's fine!