What crucial implication arises if the initial baseline AU value contained a historical error?

A systemic error would propagate into distance calculations for every galaxy measured using the ladder.

The entire cosmic distance ladder structure relies heavily on the initial, accurate calibration provided by the trigonometric parallax method, which uses the AU as its bedrock baseline distance. If the precise value established for one AU were historically flawed, this initial error would be compounded as it is used to calibrate the next rung (standard candles like Cepheids), which in turn calibrates the next rung (Type Ia Supernovae for megaparsec distances). Therefore, any slight inaccuracy in the foundational AU measurement would lead to a systemic, propagating error in the distance estimation for virtually every object measured outside the solar system, extending throughout the observable universe.