@Filfrat
I start to ask myself if we're working on the same site. The one I'm on also uses custom solutions and also got data delivered at different calendar days.
You can run live ETL multiple times on the same month with no issue. Only IRM instances for which new data get dropped into the input_area folder get outdated.
If you don't run live ETL but drop the data directly into the landing_area folder then you're not following the documented process and though shouldn't complain if things aren't working as desired.
If you drop the new data into the input_area folder and then trigger live ETL things will work. That's what we are doing.
You say that you're also building custom IRM flows. The challenge you will be facing is when you need to update an already deployed and used IRM flow definition. Basically: You can't deploy a change to an existing IRM flow definition into the same FA and with the same name without deleting all instances created using the previous version.
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