Thanks for joining us here in the QuickBooks community. It's great to see that your client corporation is a part of the QuickBooks Desktop family and I hope the program is helping ease some of the work of managing business finances.
QuickBooks records fiscal and tax years based on beginning month for that period. I hear what you're saying about the client corporation's year end being a more precise date, but that's not something that can currently be entered in the program. As a workaround, you can customize reports for the date range you want and memorize (save) them for easy access later. That way, you can see the data for the period you need even though you can't put the specific date in the settings.
Feel free to leave feedback about this for our product development team. To do so, click Help in the top menu bar > Send Feedback Online. The Product Suggestion option should do the trick.
Let me know if you have more questions. Enjoy the rest of your day!
QB does not accomodate a mid-month Year End date, making it awkward to create YE Reports. Unless it is crucial to have a FYE of March 21, I suggest applying to change the YE date to the end of a month.