You must have a nice stash of old cine literature Charlie! Thanks for putting that up.
Sopelem were a French company created in the 60s by the merger of Som Berthiot and another optical company called OPL. Rank Taylor Hobson were only the international distributers. According to Charlie's literature, the 23-115 was "a lower price zoom offered for less exacting applications than the M series". It was designed for CCTV Vidicon tube cameras of the day which had far less resolution than 16mm film, so it could be manufactured to lower specifications than the lenses made for film cameras.
The one advantage for today's market is that it would have been designed to have an image circle diameter of at least 16mm, for use with 1" Vidicon tubes, which was larger than the image circle required for 16mm cameras. So these days you could advertise it as "covering Super 16", which is what people need in order to use an old lens with some of the new Super 16 size sensor cameras that are available. Like Jean-Louis surmised, it was probably based on a 20-100 design, with a 1.15x extender added to increase the image circle.