Simply adding inactive relationships between the sales table and the date table for each date foreign key does not fully meet the goal. While inactive relationships allow for flexibility, they alone do not enable analysis over time based on all three dates simultaneously.
To achieve this, you would need to use DAX functions like USERELATIONSHIP to activate the appropriate relationship in your measures. Without this, the inactive relationships won't be utilized in your calculations, meaning that analysis based on those dates won't work as intended.