Kant claims that the three formulas also constitute a developmental progression. This strongly suggests, first, that we need all the formulas in order to have a complete account of the content of the supreme principle, and, second, that the later formulas FH and above all FA and FRE should be considered more complete and adequate statements of the law than FUL and FLN.

Kantian Ethics (2008) - Ch. 4. The Moral Law