March 16, 1998 in that example was the due date for a corporation using a calendar tax year to file its 1997 tax return.
Yes, your individual 2024 the tax return is considered to have been filed on April 15, 2025 if you filed before that date. That's why the automatic extension under section 301.9100-2 takes you to October 15, 2025 to make a statutory election. In your case, you already made the statutory election and obtained the return of contribution in March of 2025, so no 6-month extension is needed to obtain the distribution, no need for section 301.9100-2.
