What's fascinating is that I recently found some code that I believe was written in NB [1]. It's compiled to threaded code (like B) but knows about chars (like C). It doesn't quite match the story, but I don't know what else it could be

[1] https://inbox.vuxu.org/tuhs/ZKyl8drfW%2FBs1LVa@minnie.tuhs.o...