Haha this is what I was thinking. Did anyone ever actually win this prize?

That would be fraud by the radio station, wouldn't it? You can't run a contest that is impossible to win.

Giveaways like that were far less regulated at times in the past.

So? Who's gonna know?

Great way to catch forgeries

IIRC serial numbers aren't unique. Even if the DJ was doing that, there would still be a chance. (albeit extremely small)

> A unique combination of eleven numbers and letters appears twice on the front of the note. Each note has a unique serial number. The first letter of the serial number corresponds to the series year.

https://www.uscurrency.gov/denominations/bank-note-identifie...

In 2014, the Bureau of Engraving and Printing (BEP) accidentally assigned overlapping sets of serial numbers for replacements notes to its currency-printing facilities in both Washington, D.C. and Fort Worth, Texas. The overlap occurred from serial numbers B00000001* to B00250000* and B03200001* to B09600000*. On the lower right-side of the front of the note, the letters “FW” with the face plate number indicate it was printed in Fort Worth.

https://www.pmgnotes.com/news/article/9321/Duplicate-serial-...

A significant quantity of those bills has probably been pulled from circulation. One of the things the Reserve does is swap damaged bills and look for counterfeits. Every bill they destroy is another crisp bill they can return to banks without fucking with inflation.

It's not the whole story. In genuine currency, serial numbers are only unique within a series. Series 2017A and series 2021 notes can (and in fact do, since they start over at A00000001A) have identical serial numbers.

Notes prior to 1996, and $1 and $2 notes, use only a 10-digit serial number so there's repeats in new series.

You’re thinking of parallel numbers.

I can explain. But first, we have to talk about parallel universes and half-button-presses.