Month (numeric) slicer default settings

There are two ways i can think off to achive what you stated.

1. in the table that contains your date colunm add a calculated colunm for If(table1[date] < NOW() ,TRUE,FALSE)

you can then use this to filter the whole report and your slicer will shrink down to only the defaulted values

2. i always use my own date table, rather than use to built in date tables i import my own and connect all relevent dates to this table. i have a colunm in this table for month which can be used and a colunm for date_Passed that does the same check above.

i can upload a copy of my date table if you need it