Field help (CONPBLGRP) 

This column is used to enter all the LEVELS of the skill groups taken into account by the contract.

The LEVEL term indicates that all the lower levels of the skill group are taken into account if this latter is included in the covered skills.

In other words, if the totality of the generic groups had been entered in this function, the result would be equivalent to that obtained by ticking the field "All skills".