When does one storm begin and the other end? This is likely an issue they are dealing with in the state and negotiating the same with the FEMA. I see a declaration saying that "On or about, ____ (date) the state was impacted by Hurricane _____ (name of hurricane) which caused extensive damages that continued through _____ (date)."
It's likely that Louisiana State Emergency Management could basically make this a "form declaration" and make extra copies, since there is another month of hurricane season left on the calendar. Plus, with climate change, who is to say that the hurricane season will be over at the end of November?