Traditional role of the mountain dulcimer.
General mountain dulcimer or music discussions
Yes, those are excellent books and must reads for folks who want to learn about mountain dulcimer history and context. One part of your question we have not addressed is the use of European predecessors of the mountain dulcimer. Wilfried Ulrich addresses some of this in his book The Story of the Hommel. There are many such instruments in museums in Germany, Belgium, Denmark, Norway, etc.Unfortunately I am not aware of English translations of literature that describes how folks used these instruments. What is clear is that they were "folk" instruments and not considered to be of great value musically. Again, they were mostly played by folks in their own homes for their own enjoyment.
I do what to respond to Kenh's comment about amplification. The zitters used in Pennsylvania Dutch communities had feet on the bottom and were often played by placing them on tables when played. This increased the volume of the instrument. Some dulcimers builders in the late 19th century (J.E. Thomas, C.N. Prichard) made dulcimers with feet on the bottom which allowed them to be played on tables as well. It may have helped when dulcimers were used to accompany dances.
Ken
"The dulcimer sings a sweet song."
updated by @ken-longfield: 12/06/23 05:53:08PM

Here in the U.S., Jean Ritchie is one person whose family story and travels spread awareness there was such a thing as a mountain dulcimer in the central/southern Appalachians. On Jean's album The Most Dulcimer , several different styles of music are represented and it is, perhaps, my favorite record of all the music we have in the house. To me, this album offers a great point of departure for exploring various traditions related to the Appalachian dulcimer.
. I had an aunt who had perfect pitch (and a Steinway piano worth about as much as my house!). When my uncle was learning a right-hand picking pattern for the banjo, she didn't mind the repetition of the picking, but she couldn't stand that he was always practicing in the same key. So he used a capo and would just change keys every few minutes.
Since I have some issues with my right hand, (think lousy Rugby player 50+ years ago) being used to strum so I used to always string up for left handed play. A bit frustrating and all that goes with it, such as chord charts etc. So............I learned to play Galax style.......4 d strings and a noter........makes no difference how you hold that critter, works just fine. So I recommend you give that a whirl and if it doesn't suit 'ya you can return to that "bac'ards ciphering." You can also finger pick a unison Galax stringed instrument and finger dance too. Listen to Phyllis Gaskins and you'll be amazed what that style of play can do.
) we did a "quadrille." It reminded me of scenes from Jane Austen movies. We were one person short of two group of eight; I suggested calling someone in from the street, but instead they used a large balloon of Mickey Mouse as a place holder (but he couldn't go round the circle weaving between the "follows," aka the ladies. Actually I think Mickey was a follow, he would have needed to weave between the leads).