Hey Ward!

 WD> It's not certain but my bet is the 71 comes from there, someone's
 WD> knowledge/experience embedded in punchcard technology.

Possibly but from my past experience I believe it has to do with line lengths
on tty's, line printers, and the such which were as a rule 80 characters wide. 
The 'missing' 8 characters had to do with margins if I am not mistaken.  As for
the null terminator that is a hangover from strings being terminated with
nulls.  I am unsure where that idea originates but I suspect pre-F77 FORTRAN.

Life is good,
Maurice

... Don't cry for me I have vi.
--- GNU bash, version 5.0.7(1)-release (aarch64-raspi3b+-linux-gnu)