I would like once more to argue my point that, while everything is subjective, some labels have wider common ground as far as definitions go; while everyone has their own ideas and opinions, some aspects and facets is seen more often across those subjective definitions. Thus there is a narrow (or wide) ground in which most people could agree that "this is crack" or "this is dark" and so on. Those with wider common ground may have less fuzzy borders where people disagree on what is what, and vice versa.
Thusly I would say that, if an author didn't intend to/doesn't look upon their work as "crack", then for them it isn't. If someone else reads it and finds it to be "crack", then, for that reader, it is crack. There is no universal standard; retroactive labeling still only applies to the person labeling it as such - and anyone else who may share the same view; who partially or wholly inhibit the same common ground of definition.