I may be misunderstanding you here, but it sounds like you are doing a year-over-year comparison on stores that have the same time series with a forecast. In meaning, if the store was not open in the year-over-year and did not have a forecast, they were not a good candidate for the year-over-year comparison.

In my organization, we sometimes use cubes that have similar KPI's. When it comes to year-over-year, they typically pull the two sets of dates and do the comparison themselves in the front-end application, whether that be Excel or something like Tableau.

While it's certainly good practice to define that logic on the centralized reporting platform, it's also sometimes a easy one to skip over because you're just pulling two data sets and comparing them with very simple logic.

Outside of that, it sounds like you are heading in the right direction. You first must confirm if the two sets are good candidates for the year-over-year comparison. So, you defined a simple Boolean attribute that triggers the computation.