…Reverse thrust isnt taken into account in stopping distances?

In modern aircraft take off performance is usually more restrictive than landing performance on the same runway. Under JAR-OPS reversers are all considered to be inoperative for take-offs on dry or damp runways. They are allowed to be considered serviceable on wet runways but as so few aircraft these days need the preformance they are generally considered inop in order to standardise take off calculations.