It appears that subtree merge won't work on recreated split branches as they won't have a common history. The split branches must be preserved, then split will update existing branches with upstream work, and then merge will work on updated branches.
It appears that
subtree mergewon't work on recreated split branches as they won't have a common history. The split branches must be preserved, thensplitwill update existing branches with upstream work, and thenmergewill work on updated branches.