Identifying relevant rows

Daretoexplore Might be best to have an index column, but you could do it like this:

Column = 
  VAR __Cust = [Cust ID.]
  VAR __MaxDate = MAXX( FILTER( 'Table', [Cust ID.] = __Cust && [Status.] = "Entered Shop" ), [Date (UK)])
  VAR __Result = IF( [Date (UK)] = __MaxDate, 1, 0 )
RETURN
  __Result

Then for the measure:

Measure =
  VAR __Cust = MAX('Table'[Cust ID.])
  VAR __Table = SUMMARIZE( FILTER('Table', [Column] = 0), [Date (UK)] )
  VAR __Result = COUNTROWS( __Table )
RETURN
  __Result

Daretoexplore Likely need to use >= in the column formula when comparing to __MaxDate instead of =.