Why would Grant omit a river fallback from his battle account?

If falling back to Pittsburg Landing was Grant's contingency, why did he not mention it in his battle account?

His intended operation was an offensive. A fallback may have remained an emergency option that he did not regard as his battle plan.

An operational plan and a contingency answer different problems. Grant intended to attack the Confederates, while a fallback toward the river may have covered the possibility of being attacked first. That interpretation explains why an emergency withdrawal option might be absent from his account of the intended operation. It remains an inference about his thinking rather than a documented plan.