The tailwind limitation is a LANDING limitataion, ie. at touchdown. It`s quite possible that the wind at 500` may exceed the aircraft max tailwind LANDING limitation. The 500` call is a "stabilised" ie. the aircraft is in a position and configuration that WILL allow a SAFE landing, without exceeding rate of descent (pitch), bank angle, and airspeed, as it is assumed the aircraft configuration at 500` will be maintained to threshold crossing.
In situations where the tailwind IS in excess of the landing limit prior to touchdown, it is encumbent upon the PIC (and the F/O, in a 2-crew configuration) to ensure that it is not exceeded at actual touchdown, hence an approach COULD be flown to the flare before a go-around is executed.
The situation of a tailwind all the way down finals swinging to a headwind on landing (and vice versa) is a common occurence for all professional pilots, as are increasing head/tailwinds.
The final decision whether to land or go-around rests with the pilot(s), based upon the considered judgement of whether a safe landing can be made, taking into account factors such as their experience, runway condition, aircraft performance - and the "Pucker Factor"!