> one of the strongest and most widely-used programs is Stockfish [81].

Here's the citation, note the date:

> [81] The Stockfish Development Team. Stockfish: Open source chess engine, 2021. https://stockfishchess.org/.

They mention the version number only once, further down, and don't point out that it's out of date since February 2018. All other 11 mentions of it don't have the version number, like in that sentence:

> In Chess, PoG(60000,10) is stronger than Stockfish using 4 threads and one second of search time.