The organizer loosen up the rules a little bit, given that many riders didn't pick the right class (category). A rider who does not finish one race day will still be in the overall standings but they will get a time penalty for the day they didn't finish.
In order words, you have to ride the Prologue and finish at least two days of the race to be in the overall standings.
In the case where a rider does not finish two days of the race, they can ride the third day, just for fun - they won't be included in the standings.
Read more in Points 9 and 16 or Rules and Regulations.