I recently happened upon this excerpt from Basil King's steel guitar column in the April 1950 B.M.G magazine:Sebastian Müller wrote: I think that is a great idea, I am using this kind of re-entrant tuning myself on my Clinesmith 8 string. Good thing is that you don't have to relearn a tuning, you only add strings on the bottom and keep the upper 6 strings unchanged, love that concept.
With 8 strings, there is the luxury of having the full high-bass tuning and two re-entrant G strings of two different octaves on the two lowermost strings for more inversions!
The infamous Speedy West F#13th tuning E4 C#4 G#3 E3 A#2 F#2 (D#4) (F#4) is also reached by adding strings onto an existing tuning, as used by Clinesmith himself:
https://www.youtube.com/watch?v=d-cEXlDZqEE