Hello, bathmatters. I can't think that to many folk rely solely on the hard copy of the BRB. The themes are often way too arcane. Having said that, they were in the old pre-internet days. I have a collection of historic Listener puzzle books and some are virtually impossible to solve - with or without modern day aids.
It is my belief that the earlier Listener puzzles catered for a small number of elite solvers and we rarely see that level of difficulty these days, maybe three or four a year?