Two different Dates in my computer?

[carsto]

NamedRange: LastDayOfNextMonth
= DATE(YEAR(TODAY()),MONTH(TODAY())+2,1)-1


I have a spreadsheet that calculates everything off the Age of a person on the last day of Next Month, with their Birthday being in Column L

Each person age = DATEDIF(L5,LastDayOfNextMonth,"y")

Everything works great.

We had to run some backdated reports, which was no problem as I just changed the Date/Time Properties in Control Panel to an earlier date in an earlier month.

Everything calculated properly. If I changed the Date/Time Properties to December of last year it correctly calculated their birthday on the last day of January this year.

The one thing that didn’t change was the Page Header. I have &[DATE] in the header and regardless of the date I changed my computer to, somehow the header knew what the real date was.

Why / How is this?

(I don't need a solution to fixing it, it just puzzles me.)

[Special-K]

Just a shot in the dark.
Did you close Excel and reopen it?
Perhaps when Excel starts up it reads the date once from the system and not again until Excel runs the next time.
The TODAY() function could be updated differently in real time as you use it.

I have no idea if this is correct as I say just a shot in the dark.