Someday someone is going to find a 1999 Washington quarter that isn't a state quarter, even if he has to alter it.
Well... OK, I guess. Certainly it'd be simple enough to alter a 1998 into a 1999 -- just file down the lower left bit of the 8, and it becomes a 9. Now, as for a genuine, struck at the mint, 1999 eagle back quarter -- not going to happen.
I thought I heard somewhere that counterfeiters had already tried this in early '99. Went something along these lines: Before the Delaware quarters hit the market, somebody was roaming the Northeast with rolls of 1999 dated eagle reverses.
Yeah, I think I remember counterfeits early in 1999, and the rumors were that some old couple had received rolls of 1999 non state quarters at a Northeatern bank. There was a discussion about these types of coins on the board recently. Some of the ones mentioned were 1931 Standing Liberty Quarters, 1933 Washington quarters, 1964 Peace Dollars, and 1964 Franklin Halves.
If I remember correctly, there was a couple that was speending these like crazy, all over the northeast. They would even leave a roll of quarters for a tip at diners, paying for the tab with them, etc. Now, they are, presumably, doing time.