Why do you look for one consistent way of explaining how adepts gained their powers when clearly, the ways they learned their powers are as varied as the traditions used to teach magicians their spells. To use your own example of how an adept would learn Freefall, you suggested 3 ways 1) jumping off high Places 2) meditate on cosmic oneness or 3) study how feathers falls to the ground. I would say that all 3 ways have been used by some adepts to learn the same power depending on their tradition and background. A Zen adept might meditate and contemplate the oneness of the universe, a native American adept might study the way feathers fall to the ground and a sprawl kid might just jump off tall Buildings till it doesn't hurt anymore, they alle learn the same power, but in different ways that fits their individual backgrounds. Reducing it to one single way of learning an adept power takes a lot of flavour out of the game if you ask me.
That being said i'm sure that some adept powers were discovered much earlier after the awakening than others. For example the relatively simple boost and improve powers as well as reflexes, those powers likely were discovered pretty fast where as others like melanin control are likely the result of adepts experimenting with what they can do, learning to do it and then teaching others to do the same..
When it boils Down to it, then all magic in Shadowrun Works in the same way, The magician, mystic adept or adept uses their will to manipulate mana and bring about the desired effect. However the way they go about using their will is varied due to tradition, magic user type, race, gender, age, personal history.......and a hundred other different reasons that people do Things a certain way. Thats why a hermetic mage chants away in latin, a mystic adept focuses on manipulating the chi all around and in him/her and a Norse berserker adept takes certain intoxicating concoctions and calls on his gods when he goes into battle. But in essence they all.. as Medicineman so eloquently put it "They wish for it...and poof it happens"
This has been a long and somewhat roundabout way of saying that essentially, the adept has learned how to use a given power in any way that fits that particular characters or NPC's history, person, tradition..etc.
