filter by actual date

Table A

PERIOD Country Purchases

below are a series of Measures - where I've just altered the date parameter.  The return value measure in the Card visual has me baffled....

Measure = 4

ActiveByDate = CALCULATE (
    COUNTROWS('Table A'),
    FILTER('Table A',
        'Table A'[PERIOD] > 1/1/2016))

Measure = blank

ActiveByDate = CALCULATE (
    COUNTROWS('Table A'),
    FILTER('Table A',
        'Table A'[PERIOD] = 1/1/2017))

Measure = 4

ActiveByDate = CALCULATE (
    COUNTROWS('Table A'),
    FILTER('Table A',
        'Table A'[PERIOD] > 1/1/2017))