Hi David,
Originally I was doing as you mentioned, subscribing to all and filtering events based on my own logic. I thought I might have to do deal with lower traffic for events if filter at subscription time could that for me. As you mentioned events which do not contain SkillGroupNumber will be filtered out for example End/Clear. So I am reverting back to the original code.
But it could have been really usefull if instead of filtering using ';' which always act as AND we could do 'OR' between different type of filters(not the values which are alwasy ORed) within the same session.