When an employee has a change in status, such as adding or subtracting dependents, or submits a new W-4 withholding form, you'll record that information and verify that the payroll system is updated. Filing is a large part of the job.
For instance, if a policy expired on January 1, 2007, the data included on the Experience modification would comprise the period from January 1, 2003 to January 1, 2006. Experience modifiers are normally recalculated for an employer annually. Each year, a newer year's data is added to the three-year window of experience used in the calculation, and the oldest year from the prior calculation is dropped off. The other two years worth of data in the rating window are also updated on an annual basis.
* Please note: a number of these values have been rounded for simplicity. When capacity is critical you should seek out the exact conversion value. Small differences can yield a large discrepency when duplicated many times. For example, a calculation done on the number of millilters in a 55 gallon drum would result in a much different result if the base conversion number is a rounded value.