Do you always want the selected month to be in 2018? If so just add a date filter to only look at 2018.
Alternatively you can change your formula to be:
IF MONTH([Date]) = [SelectMonth] AND Month([Publishing Month]) = [SelectMonth]
and YEAR([Date]) = 2018 and YEAR([Publishing Month]) = 2018 THEN [Pageviews] END
Depending on your goal you may want to add a way for them to change the year or make you selection parameter a month/year.
Let me know if you have any questions. See attached.
SelectValuesforMonth.twbx 13.7 KB
Thank you so much. This is exactly what I was looking for.