"So your income tax return each year needs to end on the date you chose, the same date every year end. That date cannot change every year..."

That's not true.  The IRS allows certain taxpayers to adopt 52/53-week yearends, and that causes the year to end on the same day each year but not the same date each year.

(a) In general -

(1) Election. An eligible taxpayer may elect to compute its taxable income on the basis of a fiscal year that -

(i) Varies from 52 to 53 weeks;

(ii) Ends always on the same day of the week; and

(iii) Ends always on -

(A) Whatever date this same day of the week last occurs in a calendar month; or

(B) Whatever date this same day of the week falls that is the nearest to the last day of the calendar month.

(2) Effect. In the case of a taxable year described in paragraph (a)(1)(iii)(A) of this section, the year will always end within the month and may end on the last day of the month, or as many as six days before the end of the month. In the case of a taxable year described in paragraph (a)(1)(iii)(B) of this section, the year may end on the last day of the month, or as many as three days before or three days after the last day of the month.