I don't really see harmonic theory as explanatory. To me, it's just a set of labels to apply to different chords in the music. The thing is, a lot of harmonies don't get labeled by it. They're discarded as passing chords and the like. And then, after these harmonies are passed over by the theorist--and only then--he can claim that the progression follows certain rules. These rules have been recorded in a kind of flow chart for the composer to follow. But there is almost no composer who has ever followed these flow charts except if you arbitrarily cut out segments of their music. I've actually seen an ascending minor scale in which every note appeared get labeled as a V. There is a V in there somewhere. And then it was followed, some time later, by a scale degree I in the analysis. This is where the guidelines fall apart. If you can say that a V-I occurred by virtue of cutting some notes out, you can just as easily cut out a different set of notes and say that a progression from something else to I occurred. Of course, it has a great deal to do with how prominently featured the V notes were. They might have occurred on strong beats, for example, with non-V notes occurring on weak beats. That doesn't mean the other notes weren't there, though. And what is more, these other notes have an impact on the musical progression as surely as anything else. They might feature a later repeated motif, or, in light of them, the composer might wish to choose a different harmony to follow the "V" than he otherwise would have done.