You must go by everything - amber, crystals, resin,bud density, bud formation, scent, etc. One of the big mis-conceptions of this wave of shit is the Rule Of Harvesting... I see the newbies have all been trained into looking at the crystals and nothing else. Whatta Joke!
Marijuana around here is usually harvested too early as to the growers were taught wrong with an iron fist.
But yes "usually" 75%. You must watch out for strains that "look" like they are almost ready to finish and wake back up with vigour tand bright white hairs in a couple days.
Newbies are not aware of any second bursts of energy.