Thunderbirds - the meaning of FAB

We were watching "Thunderbirds" original episodes the other day, to show my kids what I used to watch when I was a boy. The show has lots of catchphrases, like "5.. 4.. 3.. 2.. 1.. Thunderbirds are go!", "Yes M'Lady", and my favourite "FAB". Of course, then the question was "What does FAB stand for?"

Wikipedia has this to say:

The characters use the radio sign-off "F.A.B." rather than "Roger" or "Over and out". Anderson was often asked what F.A.B. stood for, but stated it in fact simply stood for "fab" (short for "fabulous"), a 1960s catchphrase. During radio broadcasts it also stood for Fully Acknowledged Broadcast.

On a website where they interviewed Gerry Anderson, the producer of Thunderbirds, was this answer:

11. What does "F.A.B." stand for?

Perhaps the most frequently asked question by new THUNDERBIRDS fans, the definitive answer came from Sylvia Anderson herself during her promotional tour for her book YES, M'LADY. According to Sylvia, F.A.B. stands for...
...absolutely nothing.

It was something they made up on the spur of the moment during a writing session, Sylvia says, and it was never intended to stand for anything other than to spell out the letters of a popular British slang word--"fab"--during that era. Many people have attempted to find other meanings ("Filed, Actioned, Briefed", "Fine--Acknowledge Broadcast"), but it never meant anything other than "fabulous".

The Fun Trivia website says this:

The characters use the radio sign-off "F. A. B." rather than "Roger" or "Over and out". Anderson was often asked what F. A. B. stood for, but in fact it simply stood for "fab" (short for "fabulous"), which was a 1960s catchphrase. Later this was unofficially decided to mean Fully Advised and Briefed, following on from P-W-O-R (Proceeding With Orders Received), a similar radio confirmation code in the series Stingray. In Anderson's next series, Captain Scarlet and the Mysterons, S.I.G. (Spectrum is Green) would continue the tradition of initialled call signs.

Another saying that has lost it's meaning in the sands of time.