If you need output in a specific structure, like a table or a fixed word count, what should you do?

Say it in the prompt. Format and length are part of what you are asking for, so a request that omits them has not been fully specified — the model will pick something reasonable, and reasonable is not the same as the four-column table you needed.

Two habits make this reliable. Describe the structure concretely: name the columns, give the row order, state the word count as a number rather than as "short". And tell the model what to do rather than what to avoid — "write flowing prose paragraphs" steers better than "do not use markdown", because a prohibition rules out one option and leaves all the others open.

Fixing it afterwards does work, and it is a fair second move. As a first move it costs a round trip every time, and a reformatting pass often drops detail while it rearranges. Specifying up front is the same information delivered earlier, and it is the difference between one response and three.