Calculate difference between consecutive rows filtered by SELECT DISTINCT

I need to calculate the difference between values in consecutive rows and display the value in the 2nd of each pair of rows, apparently without the help of an index.

Specifically, I created a calculated column, Workdays Since Filed, and now want to subtract the Row 1 Workdays value from the Row 2 value and display the result in Row 2 as a calculated measure.  

Values in red show how it should work:

Getting the "Days Between" calculation is complicated by the filters on this table that made using an index difficult. The main filter is PERMIT_ID and that could be indexed using dynamic filtering tricks I saw on other posts in this forum, but the filter that really hoses things up is a SELECT DISTINCT that removes duplicate rows from display when multiple new documents are received in the same day.

So the user sees this: 

Behind the scenes, the table actually looks like this:

I worked through solutions on about 5 similar posts but didn't find one that fit this issue specifically. Any ideas? 

Thanks,

Allison