I have a Month field, and if I'm using a trigger to select only the Months until Last_Month.
I have Months until May - but I'm using a trigger to get only the Months until April. Suppose if the data is updated and now I have Months until December - then the trigger should automatically select Months until November.
My suggestion is a variable that contains the desired threshold value. Then use the variable in the search string when applying a selection action. See attached example where a button triggers selecting all YearMonth values besides the latest one.
Note that I use YearMonth and not Month, as a selection in Month would for example exclude the month in every year. YearMonth only exclude one specific month.