I don't think your logbook is the only thing they look at. They may ask you directly about your attendance. If something seems fishy, they will dig further to find out if there is an issue. If you didn't fly because you were on reserve or you were senior enough, then there won't be an issue. However, the guy who shows up to get a seniority number and then doesn't show back up to the airline until his upgrade class is going to have to have a pretty good story to explain himself.