Weird.....I don't have a 9/30 Corp but I changed the FYE on one and it came up with 1.15.19.
IF you really care, maybe copy the file and play in that one by removing/changing the month-end, process the return, even reboot in between?

You can always edit the letter - but I seldom resort to that.  I just don't like it, altho Lacerte does give a good reminder that you are using an edited letter.