Present the last month data

gilr1975 

I suggest you to add a date column

Measure = 
VAR d=max('Table'[date])
Return maxx(FILTER('Table','Table'[date]=d),'Table'[accumulates])

gilr1975 

I am not sure how your data looks like. You still want the number of max month? Are there duplicated employees in the table for each month?

I created test data.

Measure = 
VAR d=max('Table'[date])
Return calculate(DISTINCTCOUNT('Table'[employee]),FILTER('Table','Table'[date]=d))

It will be better if you share the excel screenshot of your data structure and expected results.