Daniel Bowen wrote:

In those circumstances though, I'm still not clear on why there was a need
for paper-trails.

I suspect it may have been more a matter of the BBC paperwork and red-tape
department having unlimited budget and space for storage, and the
department
looking after the old tapes/films not.

This is another myth - until 1978 there *wasn't* a department with a job to
"look after" the old tapes. Engineering just had a job of storing them until
they were next used. The Film Library was not evisaged as a mass archive of
old programmes, whilst BBC Enterprises only seemed to keep stock they were
selling.