Barbara I would like to help but most of my information relates to Scotland from early days. I do not know much about the US family and there are some well researched & knowledgeable contributors to the site.
The US family's sheer size and complexity is intimidating. It would take enormous effort to draw it all together. There must have been a very large number of seed emigrant families to have created such a volume.
At a guess the family is not nearly as relatively common in Scotland as it has become in the US.

My GGGGrandfather died at Galston Scotland about 1855. He had 13 children by 2 different wives and at least some of these children married and had their families in the same small town. There was at least one other unrelated Caldwell family living in the town at that time.

My parents moved to Galston in 1949 when I was very young quite unaware of its connection with our family. When asked in the 1980's my mother said that as far as she knew we were the only Caldwell family living in the area approximately 100 years later. Many had emigrated.

The late Mrs Lesley Gordon of Cowden Cleuch made a study of wills and she pieced together many genealogical charts which she kindly made available to me.

Mrs Gordon was always happy to help where she could. Wills mean property and obviously they relate to the better off Caldwell's consquently the information may not help all.

They principally relate to the Lochwinnoch area and the Ayr area and cover the period roughtly 1500-1700. I am happy to scan the lists for those that can give me definite leads into this area at about the right time.

Bear in mind that most of the emigrants were poor weavers, farm-hands or coal miners fallen on hard times. The better-off stayed put. The former probably had no wills.