I decided to follow up on the "infamous APL". I thought that the early matrix-sig participant might have acknowledged the APL influence more directly.

That doesn't appear to be the case. That is, Jim Hugunin's paper "Extending Python for Numerical Computation", from the December 1995 Python Workshop, at https://legacy.python.org/workshops/1995-12/papers/hugunin.h... makes no mention of APL.

It starts:

> There are a huge collection of existing numeric programming languages, both commercial (Matlab, S-PLUS, IDL) and free ( Octave, RLaB, Yorick , BASIS , Gnudl , ...). Why on earth would I want to go out and create a new one?

> I've used almost all of the available numerical languages at one time or another over the past 8 years.

APL and its descendants like J and K aren't mentioned.