Hi Dawn,
This is a pretty simple one.
You have the right formula, just not the correct context of the calculation.
Instead of accident_date column in the table you require the dates column.
If you have a look at the formula and the FILTER part. You are removing context from the date table. But in your table there is no column from the actual date table. So this part of the formula is doing nothing in the current state.
Also instead of using all, consider using ALLSELECTED also.
See what I mean here