You can't use a relative filter, because you can't exclude the latest month, only include it.
Instead a calculation like
if datediff('month',today(),[DISCH_MONTH])=0 then "latest" else "Not Latest" end
used as a filter could work. It the latest month isn't classed as the same month as today, then you may have to use a table calc:
if datediff('month',attr([DISCH_MONTH]),window_max(max[DISCH_MONTH))=0 then "latest" else "Not Latest" end
You would have to check that for the right result - that will always scrub an entire month (not calendar month) off.
To do calendar month, you would look to compare datetrunc('month',[DATES])...