I assume you have 3 date attributes in the fact table associated with Calendar, Accident and Policy years. If not, that should be your objective. It is worthwhile to determine these time variables in advance and not on the fly at query time. So, at the Claim Line (most detailed) level, create/populate three date/time attributes. If the day of the month is not important, you can certainly have something like PolicyYYYYMM.
Then, there are two options. One, have a Calendar table as your time dimension. In the calendar, you can take care of things like fiscal year and month, weeks assigned to quarters, monthly close and process dates, etc. The second option is to simply define three time dimensions, one for each of the three dates (Cal, Acc, Pol) in the fact table.
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