The calendar that matters is the decision calendar
Travel businesses plan around when people travel. Their marketing should be planned around when people decide, and the gap between the two is often several months. A family choosing a European summer is having that conversation in the winter, once school dates are published and leave is provisional. A couple booking a beach week is deciding on a Sunday evening about three weeks out. A pilgrimage group is organised by one determined person who starts a full season ahead. An agency running the same broadcast schedule across all of them is reaching each group at the wrong time.
The remedy is unglamorous. Write down every destination the agency sells, the weeks when enquiries for it historically arrive, the weeks when travel happens and the visa or permit lead time. That sheet becomes the campaign calendar, and it immediately tells you which months are quiet, which are overloaded, and which destination is being promoted a month too late every single year.