“In principle, I could have used the same engine itself as the teacher, but just to save on wall clock time I used Stockfish. This reduced the wall-clock time from ~4000 1996-core-years (something entirely doable in 1996---but sadly not something I can do with my single lonely desktop) to just a few days on a modern desktop running a modern engine.”

I see no reason to doubt the author here.

Stash has never adopted NNUE and breaks 3k with ease

It's also great reference engine with all of the pinned tags of its evolution.

https://github.com/mhouppin/stash-bot

https://chessprogramming.org/Automated_Tuning has excellent history. Still substantial compute on tuning, but viable.

NNUE was added to Stockfish in 2020. Although this was a big improvement, it was already extremely strong before that. With plain hold hand-coded logic as a board evaluation function.

You could have used one or more Deep Blue computers as the teacher model, or just a cluster of regular PCs doing very deep searches.

Doesn't the author address this point? They speculate that it could be attained through self play back then using a ton of 1996 compute and time, but it's theoretically possible.