CAVOK has a specific definition in terms of a cloud base and presence of CBs, sandstorms, etc so it may have been 9999 but potentially not CAVOK.
CAVOK is visibility greater or equal to 10 km, no cumulonimbus and no cloud below 5000ft or highest MSA (whichever is the greater) and no sig weather.
NSC is No Significant Cloud.
Thus you could be in viz condition of 9999 but have cloud below 5000ft.