Not sure what your question is, but filter is different to parameter, e.g. if you have 3 rows,
when you do a filter, B, only the row with value B will be keep in your view.
While parameter is different, when you parameter value B, and it doesn't impact any rows above, and when you do a comparison between parameter and the data, like if value = parameter then 1 else 0 end.
then the result will return 3 rows as
Hope this makes sense.
I will suggest to introduce a date parameter as date selection in this case.
the date parameter is only controlling the 12months previous data