Dutch to English Bus/Financial Finance (general) Pension Fund

I am currently working on a document related to a pension fund for employees. I translated **pensioensalaris** as pensionable salary, which I thought was correct, especially if you consider this part taken from the text (definition of terms):

**Pensioensalaris**
De som van 13 maal de vastgestelde maandverdienste en de vastgestelde vakantietoeslag.

I have now come across the following section, however, which has completely taken the wind from my sails:

De **pensioengrondslag** is gelijk aan het pensioensalaris verminderd met de franchise. Een negatieve pensioengrondslag wordt gelijk gesteld aan nul.

So clearly there is a difference between **pensioengrondslag** and **pensioensalaris**, which I think is pretty well defined here. I am pretty sure that pensioengrondslag = pensionable salary, which is also conmfirmed by Van Dale, but then what about pensioensalaris?

TIA