Where test weight comes into play on estimating  yield is if a guy has no scale and hauls nothing into town. Just fills the bin. Lets say he filled the 100000 bushel bin with 56 pound corn in 2024 off 500 acres. Hauled 100000 bushel to town in June of 2025. This equals 200 bushel per acre. Now in 2025 fills same bin with 54 pound corn. But never checked TW. He is thinking he has 100000 bushel, same yield as last year. Now he hauls his 54 TW corn to town to fill his June 2026 contract. Only hauls 96400 bushel out of the same bin and it is empty. 3600 less bushel then last year off the same 500 acres equal 7.2 less bushel per acre then 2024 crop.  This is how Test Weight  can come into play and people over estimate how much corn they have to sell and find them selves short