In the old days, 3-c knowledge was not accessible, as ray noted. It's true that if you paid the time and asked for help you'd get it if you were a hack, but the serious knowledge was not easily accessible. I can remember a moment when I was an aspiring 3-c player years ago (I was a hack, I averaged .330 over 10 handicapped weekly tourneys). I remember studying a shot for a while, and a solid player (prob .650 at the time) said "this is a hanger. double kiss straight back with a tip of left english and double the rail. . ." I did just that and like magic I made the billiard. The problem back then was that a lot of the advice you got was from .5 at best players that didn't even know how little they knew. I used to play with a guy that was in his 70's and was a good friend of Boston Shorty. I'd play with him and he'd be obsessed with teaching me diamond systems, but he was a terrible teacher, and I wasted a lot of time humoring him. He would basically mutter to himself, tell me where to hit the rail and with what english, say "so 35 goes to 70, 70 goes to 15, adjust 1/4 diamond. . . .hit here." etc. These days 3-c players play so f'n good, and you can just watch them on youtube all day. Back then, you had to pay $30 for a vhs accustats tape, and that was a lot better than pre-vcr's lol.
A few years ago I was in a billiard room (which closed maybe two years ago). Mike dechaine came in and was playing the owner even, who was not young and maybe a .5. I think Mike lost, but I remember him saying how if he played for 6 months he could be top 10 in the u.s. easily. When a few billiard players were challenging him on that, he said confidently "I know my stroke." There's a lot of knowledge in 3-c, it's like 1p, but mike did end up playing some 3-c when he was living near mazin shooni's room, and i must say, he plays pretty good lol. . . .
https://www.youtube.com/watch?v=zs77Q_W61sE