I think that a "bookend" note is the same as an "almost radar", as has been pointed out. Your note may be described as a bookend with three digits-001xy100. There are people on
ebay selling bookends of only two digits-00wxyz00. Of course if the bookend were four digits, it wouldn't be a bookend at all, but a true radar.
I think that the "bookend" term is one of many made up by
ebay sellers to attribute something special to a statistically common occurrence. As interesting as it is, I personally don't give it any extra value. If you search through enough bills, you'll find plenty of "almost". That being said, if it's worth $1.01 to you it's worth keeping!
-wheatiefan