Can you provide a sample workbook with your raw data?
It's a little unclear what you want from your description and your data.
Suppose you had a record with Created = 1/1/2017, Ended At = null, Interval = year
Then usually Current Period Start = 1/1/2019, and Current Period End = 1/1/2020. But it looks like there are sometimes when the current period is shifted a little bit, I'm not sure why.
You want this to count as an N on 1/1/2017, and an R on 1/1/2019. Is that right? Are we supposed to count something on 1/1/2018?
If we're not supposed to count something on 1/1/2018, then you can use a pivot or a union to get two copies of the table, one with Created as the date and the other as Current Period Start as the date. Then just count how many events happened on the date.