Unsolvable Mystery Revealed: One-time Enigma or Clever Riddle? Can You Crack it?

Unsolvable Mystery Revealed: One-time Enigma or Clever Riddle? Can You Crack it? - ONEANDDONE
Never to be repeated ... or an apt pronouncement after following the instructions sequentially in 17-, 25-, 39- and 49-Across?

Crossword Clue: Never to be repeated … or an apt pronouncement after following the instructions sequentially in 17-, 25-, 39- and 49-Across?
ONEANDDONE

Explained 2023-08-13 by William Cross

Crossword: New York Times

Date of crossword: 2023-08-14