Running Script On Fiscal Or Calendar Date Whichever Is Later

I am working on creating a new report that has to get its date from several different tables. Some of these tables update at the beginning of the fiscal month, others at the beginning of the calendar month (). My goal is to develop a stored proc that will run once a month, get all the data from the various sources, and insert into a history table. An SSRS report will generate off of the data in this history table so users can see a running history of the data. I am having trouble creating a way to determine this though. Fiscal months always start on a Sunday. We have a calendar table that translates each date into the fiscal day, fiscal month, etc. Changing the legacy scripts to run on fiscal instead of calendar is not an option.

Idea 1: Wrap the script in an IF statement that will determine the date of last day of the previous calendar month, and the date of the last day of the previous fiscal month, and if current date is greater than both of those, then run the script. But this runs into issues because the current date could be in a different calendar month than fiscal month causing the idea of "previous month" to be incongruent.

Idea 2: Find the current day of year, then if this is greater than last day of the previous fiscal and calendar months, run script. Issue this this is in january, fiscal day might be 2 but calendar day might be 364, so it will never run.