This is what the document says. I assume this means if they have not completed the eligibility requirements by their anniversary date it switches to calendar year.
The Plan defines "month of service" as a calendar month in which you complete at least 83 hours of
service. Furthermore, the Plan defines "year of service" as a 12-month period in which you work at
least 1,000 hours of service for the Employer. The first eligibility service period starts on your first
day of employment with the Employer. For example, if you begin work on February 15, work 80
hours in February, and work at least 83 hours in each of the months of March through August, you
would enter the Plan on October 1. If you did not complete six months of service by the following
February 14 but did complete 1,000 hours of service by that date, then you would enter the Plan on
the April 1 immediately following the completion of the one year of service.