"Definite ninety-nine" - UK English meaning

Solution 1:

It could be @Barmar was right by asserting that the woman in the Judas Priest song is a tribute to the female spy known as Agent 99, in the American T.V. comedy show Get Smart. The show ran from September 18, 1965 to May 15, 1970 and Judas Priest's debut album was released in 1974, so the timeline fits. Unlike another user, Greycat, I could not find any documented proof as to when the series was aired in the UK, but transatlantic flights were fairly common during the 60s and 70s and who's to say that the group were not fans of the cult show?

I realize it's a long shot but it is a plausible shot, and one which might explain the meaning of Definite ninety-nine.

Wikipedia informs:

Agent 99 (Barbara Feldon) is the tall, beautiful female agent whose appearance is useful in undercover operations. Generally, Agent 99 is more competent than Smart, but Smart saves her life in several episodes.

One of the show's many catchphrases was

Good thinking, 99! (usually commented by Smart) _Wikiquote

Otherwise on a more practical note, I'm inclined to think the phrase definite ninety-nine is Judas Priest's own unique way of saying that the woman is definitely a 9. Ninety-nine makes her close to being perfection, and indeed the band heap their praises on her

Man eatin' momma, steam driven hammer
Sorts the men out from the boys
Takes no messin', all in wrestlin'
[...]
She's a classy, flashy, lassy
Imitation sapphire shine
Two faced liar, full of fire
[....]
Barroom fighter
Ten pint a nighter
Definite ninety-nine
[...]