Remember: the value for StartWith is order of the axis value, not exact value (StartWidth):
=DatePart("ww", today(), FirstDayOfWeek.Monday, FirstWeekOfYear.System ) -min(Fields!skp.Value)).
=CountDistinct( IIF(Fields!skp.Value <= DatePart("ww", today(), FirstDayOfWeek.Monday, FirstWeekOfYear.System ), Fields!skp.Value, nothing) )