A lot of people. It just took YEARS of exploration and trial and error, as well as word of mouth at school. I beat Legend of Zelda quest 1 and 2 with no guide(it just took YEARS). I beat Castlevania 2 with no guide.
It was amazing how many people actually drew out their own maps back in the day. The network of information back then was almost all word of mouth. Some days, you would play with the intention of burning every single bush on the screens. Some days you would bomb every wall in the game.
Castlevania 2 was actually easy as heck and only took months, as opposed to the years of Zelda. The only problem most people had was the Cliff/Red Crystal was so vague.
And it was not really a problem because you could literally skip figuring that part out by performing the very hard jump or die in Camilla cemetery that EVERYONE tried. It took you to the same part the warp did and a perfect jump could make it. That's how I did it.
The Red Crystal thingy itself was not that hard to figure out. My friend did. Kneeling with the Blue Crystal in the appointed Lake place was something that you were told to do. The townsfolk tells you to "hit Deborah cliff with your head to make a hole". The book tells you ""Wait for a soul with a red crystal on Deborah Cliff."
Eventually, he would try kneeling like we did at the lake.
Having the heart equipped to get somewhere else on the Ferry was something that happened accidentally to most people. At some point, you would equip every different item in the game trying to figure out what it did. Some were obvious like the Bone and eye. Others you just kept on to figure out.
