Slightly OT since I didn't just learn it, but following on . . .
The F-35 Lightning II , AKA JSF, should have been the F-24 (the next unused designation in the series of US fighters), but the US undersecretary for defence confused the designation of its experimental precursor the X-35 (on a different series of numbers) with the production aircraft designations at a press conference in 2001.
This annoyed the manufacturers & the USAF, USN & USMC, which had all been assuming it would be called F-24 & had been using that term in internal documents. The office that assigns designations recommended that F-24 should be used. But to no avail: F-35 stuck, & was officially adopted.