Why not a YF-24 and YF-25 designation?

[PolluxDeltaSeven]

But we have to admit that even the X- designation was a little bit curious.
Why not a YF-24 and YF-25 designation?

I remember back in 2000 that I red in a French newspaper that this X- designation could be a good way to "hide" a already operationnal F-24, a kind of Black Program fighter.
I can't remember what this fictious fighter was based on? Maybe a kind of A-12 derivative, or F-23, I can't remember.

[RLBH]

This site is very comprehensive on the quirks of the designation system, and all the new and exciting ways that it's been ignored.

http://www.designation-systems.net/usmilav/index.html

Actually, F-111 ought really to be B-1, seeing as the '111' was from the Air Force pre-1962 system, but the designation was introduced more-or-less concurrently with the MDS designation. But, F-111 would certainly be correct pre-1962...

F-15E isn't too bad, though, as it does retain significant air-to-air capability (I believe it gets used as such quite frequently) and the 'F' designation provides for air-to-ground capability. F/A is just politics.

[rob1bureau]

But we have to admit that even the X- designation was a little bit curious.
Why not a YF-24 and YF-25 designation?

I remember back in 2000 that I red in a French newspaper that this X- designation could be a good way to "hide" a already operationnal F-24, a kind of Black Program fighter.
I can't remember what this fictious fighter was based on? Maybe a kind of A-12 derivative, or F-23, I can't remember.

An interesting data was given on the official page of a USAF officier : http://web.archive.org/web/20050318164828/http://www.edwards.af.mil/units/bio/lanni-bio.html. See the list of aircrafts flown...

(By pure coincidence, that occurence has been removed on the later versions of Col Lanni's bio - see http://www.af.mil/bios/bio.asp?bioID=10031
.)