Thanks, David!

I now have two of these "Buschian Vademecum-y" casket sets, both with a barrel and 7 cells from 15 to 75cm focal lengths. Neither of them have the corrector plates, and neither has the "Busch" name on them anywhere. But both are Aplanats, and to all practical purposes identical - to each other and the "original".

I've hunted around and got a scan of the original instrucions. Then I set up a simple spreadsheet to calculate apertures and focal lengths disregarding cell spacing and front cell enlargement effects on the virtual aperture - and got exactly the same results!

This one is from a different casket set, which has one rear cell which seems to have been designed for maximum coma: