How to flag times that were in the prior reporting period that are not in the current

[Anonymous]

I have a data table with data with current and prior days sales.  I am looking for a formula idea that I can use to flag (or specically count the number of unique items) that were in the prior reporting period and are not in the current period.  There is not data records for every day so I assigned a number to the reporting periods in reverse order from the most current (MAX) date.  Basically I need to see what items are not in the MAX date (1) but were in the prior date (2).

[Anonymous]

Here's a full analysis of your problem and much more:

https://www.daxpatterns.com/new-and-returning-customers/

For customers just substitute products.

Best

Darek