in DAX count distinct values from previous dates missing in current period

I have following table:

id  date

1a  01.01.19

1a  02.01.19

2a  03.01.19

3a  04.01.19

4a  02.02.19

4a  03.02.19

2a  04.02.19

I'm trying to calculate amount of distinct ID's in previous period which are not appearing in selected period.

So selecting Feb'2019 should return - 2 ("1a" and "3a" are counted since they are not appearing in the current period, but appeared in previous period (so in Jan))