DatesInPeriod within Selected Value Range

Thank you, this is making sense to me for when a user is only using a month slicer. The slicer I am using gives a period and then using that period there is a start and end date

I have a special dates table to account for what period each date falls in, I then have that related to our main date table which holds the unique values and that then relates to my data

Thinking I could do something with your logic above that involves using my start of this period, end of this period measures? 

Thanks again! I will be saving your measure above for when I am working with standard periods.