Recently a couple of races have been disrupted by people not part of the event inadvertently getting in the way/helping.
The first time I was with a breakaway group doing about 4w/kg, we came round a corner as we caught a rider just riding along minding his own business at 3w/kgish …the others in the group sailed past but I got ‘stuck’ in his draft and had to put out a good 10 seconds of 6w/kg to break free. By this time the other 3 guys had opened up a 15 meter gap, and that was all she wrote for me staying with them that day!
The next ride the category I was racing in had been split apart early on, leaving riders all over the course. A guy on a TT bike who was doing a workout (seemed to be long steady riding at 3.2) was randomly riding the same course, and of course everyone he overtook jumped in his draft and got an easier ride onto the wheel of the next guy in the race! This ended up with a group of about 20 people who would not necessarily have ever caught each other again being given a tow back into contention for top 10 places.
In short, riders not in the event module should not be taken into account for the physics of the event. Keep them on the course, but make them not hold up/give drafts to people racing.