Work with the example
How should four report columns continue from October into January? B3 supplies a date within the first month. B5 normalizes that date to day 1; C5 advances one month with EDATE and is filled right. The header cells stay numeric dates.
| Anchor | Four header displays |
|---|---|
| 2026-10-15 | 2026-10, 2026-11, 2026-12, 2027-01 |
| Counts under columns | 12,9,15,8 pages |
Edit the working cells
B5 uses =IF(ISNUMBER(B3);DATE(YEAR(B3);MONTH(B3);1);"Date missing"). C5 uses guarded EDATE(B5;1), filled through E5; use yyyy-mm display. Change B3 to 2026-12-15: Dec 2026 through Mar 2027. A fresh 2028-01-31 gives Jan 1,Feb 1,Mar 1,Apr 1. Clearing B3 gives Date missing in all four headers.
Check the failure case
B9 adds 30 days, which is not the same as a calendar month. Also, changing headers does not move the old 12,9,15,8 counts: enter data for the newly shown periods before reporting them.
Why does a January 31 anchor not create a missing February 31 problem here?
Show the worked answer
The formula explicitly normalizes the anchor to January 1 before advancing months.