Checked this thread again, very late on, and found the last comment.
The 24 exposure kit was "peculiar" to the Rolleicord only, and not the Rolleiflex. to my knowledge, no Rolleiflex ever had a 16 or 24 exposure kit, only the Rolleikin for 35mm. I had a Rolleicord in the early '80s and used the 16 and 24 kits, with (I suspect) some film flattening problems, possibly with my camera back. In due course I traded the 'cord with the two kits for a Rolleiflex T which I still have and use. It has a 16 exposure kit which looks very similar to the Rolleicord one, but according to Rollei books I have in my library, the two kits are not interchangeable. (A useful tip here, if your 16 kit has a counter wheel marked '16', then it is a Rolleicord kit - no wheel is needed for the Rolleiflex 16 kit.)
A recent lucky find in a local charity shop was an original (circa 1950s, I think, but may be older) Rolleiflex 35mm back, a complete kit. No counter needed as the actual counter was built into the back. It fits all my Rolleis perfectly. I've yet to test it for film image spacing, but it looks as new. I just checked the box the kit came with and saw the original brochure is dated 06-49, so mid 1949. I must take it out and try it soon.
Rolleiflexes never cease to amaze...