There are times when we'd rather not say precisely what we mean/know (e.g. detailed descriptions of illness and accident). At such times we can use euphemisms - figures of speech which consist in the substitution of a word or expression of comparatively favourable implication or less unpleasant associations, instead of the harsher or more offensive one that would more precisely designate what is intended (OED).
The 'second meanings' of 'explicit', 'classified' and 'graphic' would seem to me, at least some of the time, to be euphemisms. Notice that when they are used euphemistically their meaning is different to their usual, dictionary definition:
Would that movie be OK for the kids ? Hmm, I don't think so it was a rom-com and some of the scenes were pretty explicit. (i.e. too much sex)
(Mates chatting) So, how often have you been pulled over for speeding? Sorry, that information's classified. (i.e. none of your business)
He described the accident, graphically. (i.e. in shocking and excessive detail)