— but that’s 5,2,3,4! Yes: FACTS (5) IN (2) THE (3) CASE (4).
— but that’s 4,2,3.
The expression comes from the milling industry. "Grist" refers to the grain that is brought to a mill to be ground into flour. Therefore, any grain—no matter its quality—was seen as useful material that kept the mill running and the miller in business.
The answer to the crossword clue "Useful material or knowledge" with the letter count (5, 2, 3, 4) GRIST TO THE MILL