Spanish to English Bus/Financial Insurance

Full context: "Si antes del Accidente el Asegurado presentaba defectos corporales, la invalidez causada por dicho accidente no podrá ser clasificada en un grado mayor al que resultaría si la víctima fuera una persona normal desde el punto de vista de la integridad corporal. La impotencia funcional absoluta y permanente en el miembro es asimilable a la pérdida total del mismo."

This is part of an Accident Policy, for a company in Spain (the company is of French origin, if that's relevant), in the section where the % of the sum assured that is payable on partial disability - loss of one leg, or blindness in one eye, etc is specified.

I feel that it means that if your leg was already paralysed, then you don't get any payment if it is subsequently severed in an accident, but a) am I right? b) how do insurers word this???