How to identify new 'Lead Person' by date whom have not existed before?

[D_PBI]

Hi all,
Take a look at my starting data (below). For demonstration purposes, it's a pretty simple dataset.

All the columns belong to a single table (Table A) except for the 'Week Beginning' column. This column belongs to the Table Date table which, through a relationship, filters Table A.

What I would like to do is use a 'Line and stacked column chart' visual to show the following:
1) The distinct count of Reference Numbers by Week Beginning, split by Class.

2) A line showing the distinct count of new Lead Person(s) by Week Beginning.
3) If possible, show a second line on the same visual (don't worry if this isn't possible) that shows the count of all Lead Person(s) by Week Beginning.
4) When you hover-over each line it shows a list of Lead Person names for new Lead Person(s) (for 3), or a list of all Lead Person(s) (for 4).

Maybe the mocked-up end-result visual will help explain what I am trying to achieve.

Reflecting the sample dataset, to break it down:
Week Beginning 11/05/2020 there were 2 unique Class A Reference Numbers, 2 unique Class B Reference Number, 3 all Lead Persons, and 3 new Lead Persons.

Week Beginning 18/05/2020 there were 2 unique Class A Reference Numbers, 2 unique Class B Reference Numbers, 4 all Lead Persons, and 3 new Lead Persons.

Week Beginning 25/05/2020 there were 2 unique Class A Reference Numbers, 4 unique Class B Reference Numbers, 5 all Lead Persons, and 2 new Lead Persons.

When I hover-over the blue line a tool-text tip appears for all unique Lead Person by Week Beginning, and when I hover-over the red line a tool-text tip appears for new unique Lead Person by Week Beginning:
Week Beginning 11/05/2020 For all unique Lead Person - Dave, Ben, Mike are listed. For new unique Lead Person Dave, Ben, Mike are listed.
Week Beginning 18/05/2020 For all unique Lead Person - Jane, Paul, Mike, Sharon are listed. For new unique Lead Person Jane, Paul, Sharon are listed.
Week Beginning 25/05/2020 For all unique Lead Person - Sharon, Mike, Peter, Dave, Steve are listed. For new unique Lead Person Peter, Steve are listed.

How can I produce this wanted visual/measure using DAX?

If you can provide me the measure details I'd be most grateful.
Thanks.

[dax · Accepted solution]

Hi @D_PBI , 

I create an index column to calculate new person, you could refer to my sample for details. 

Best Regards,
Zoe Zhi

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

[D_PBI]

@dax - thanks so much for your help. I was stumped on achieving this but having followed your approach, it seems all so easy. Thanks again, much appreacited.

[D_PBI]

Bump - anyone please?