Only if you're afraid to spend them. Bills are dated by "series" and not by the year they were printed. A series currently begins when a new Treasury Secretary takes office and ends when they leave. In the past, series were even longer - the 1935 $1 bill series was printed until the mid-1960s, for example!
Yes, bills with misprints are often more valuable to collectors. The specific value would depend on the severity of the misprint and the condition of the bill. It is advisable to consult with a currency expert or collector to determine its potential worth.
20.00 dollar bill 2 face
What is the difference in a 2004 twenty dollar bill and a 2004A twenty dollar bill?
There are many possible types of misprints. Please post a new and separate question that describes the misprint.
$20
Ah, 20 dollars.
$20 Dollars.
nothing
$20 bills don't have pictures of airplanes on them.
Please post a new question with the bill's date
If you have four of them, then the set is worth $80.
The security thread was first used in the Series 1990 notes
The Australian Koala series of coins were only ever minted in platinum and the Twenty-Five Dollar coin was only ever issued as part of a set.