If I understand correctly, the objective is to prompt the users to determine which months are to be included in the resulting data set. This can be done by either:
(1) Manually via selecting individual months within a single year
(i) Can more than one be selected at a time?
(2) Dynamically via selecting a YTD option that will select all individual months within that year
(i) Assumption that all years other than 2021 would automatically select 12 months
(ii) Assumption that in the current year (2021) only the months available would be automatically selected (E.g. if this was run on March 10th, only January, February)
Now when you say YTD. Are you going to have a resulting data set that shows each month stacked (meaning individual rows for each month) or will the 12 months of data be aggregated? Without knowing the nature of the data just trying to visualize what we're working with to determine an approach. In short, if you could show some sample/mocked up data before and after would be useful to help understand the objective.