There would be a limit to the amount of time a crop could be kept in darkness and still see an increased level of THC.
 
Plants will only survive in total darkness for a certain period of time and after that they will die and all plant processes will stop and over all degradation will begin.
 
It is common knowledge among experienced growers and experts that some light rays degrade THC.
It is also known that during periods of darkness the lost THC will be replenished and there will also be an increase bringing the overall levels to a higher point than before the degradation.
That is of course why THC levels do increase as flowering advances until maturity, that is as long as no conditions exist that would otherwise also degrade the levels of THC.
 
So since THC is created and builds up mostly during periods of darkness why would not extending the final period of darkness to the limits where a plant will still create THC and increase its level of THC without degradation be beneficial in at least some strains?
There would be a continuation of THC production without the normal subsequent loss of THC during periods of light. That could only result in an over all increase of THC, at least in some strains as tests have proven.