Thank you all for your thoughtful responses!
Doug: I took your advice to heart and took my concertina to a hooley---even though I thought I wasn't ready. It was great! So much more fun (for me) to snuggle up in the corner with the band than to be sweating it out on the dance floor. And playing next to another concertina made me realize that my mistakes weren't unforgivable and that I could catch up. So thanks!
Bill N: Good advice regarding muscle plasticity vs muscle memory. The other concertinist at the hooley made fingering suggestions that make good sense and I'll have to work against muscle memory to incorporate. So, I'll work on plasticity.
Mr. Jones: You bring up a good point. Ya gotta be able to see the big picture in order to best map out the fingerings for phrasing. It's good that so much of the Irish music has a loose pattern to it, so I usually have a pretty good idea of where things are going note-wise. Just got to get my fingers to figure things out.
Jim: I did not know about using the stronger finger, and that concept has greatly changed the way I look at the buttons. Makes great sense. I will try out your suggested fingerings, they sound like they make a whole lot of sense.
Again, thank you all. Sorry for the delay in my reply, I've been taking a few days to let your advice soak in. Now, back to playing, everyone!