The David Caldwell who you refer to is the brother of my Great Grandfather Alexander William Caldwell (1889-1982). I have input as much of the tree as I know but have never had any knowledge of what happened to David Caldwell when he emigrated to the USA. Lots of information about my own line but afraid cant help with David. I did see on another tree recently that David had 2 daughters, clearly you must be the son of one of them.
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