Vacations are based on years of service. You are absolutely correct. But, you are allowed to bid a vacation in the calendar year that you earn it. So, if you "earn" a vacation in November of a year, you can take it anytime previous to it in the same year.

We all bid for vacations at the same time (within a few weeks of eachother). If it were truly based just on years of service, you would bid only on your anniversary date.

The contract, and company, allow you to bid for a vacation in a year that you will earn it. So, if you earn 2 weeks of vacation anytime in 2017, then you are allowed to bid for 2 weeks of vacation in 2017. You can take them in January and February, even though your anniversary date is in November.

The only catch is, if you leave before your anniversary date, you have to pay back the time that you took that you didn't earn.