First of all, Alucard seems to be two tiles wide and three tall. When he jumps his feet are 4 tiles higher than they were when he started. This means that the shortest ceiling is 3 tiles from the floor and he can jump onto a tile that has a top that's 4 tiles off the floor.
Sometimes a flight of stairs or a hole in the floor is good enough to go up. The second image has three tiles from the top of the stairs to the bottom of the next floor - just short enough to jump up.
Jumping back and forth between side platforms is the most common. These pictures show that sometimes it's more obvious than other times.
Here's a short series of jump-through blocks.
This could be either a series of jump-through blocks or jumping from side to side depending on how you look at it. This pattern shows up in a few places.
There are also a few places with moving platforms to bring you up or down.
And this is my favorite example: a weird mix of side to side, stairs, and just jumping up through a hole in the floor. I don't remember if it's here or another place but I think you can't get to some of the non-essential side platforms until you have double-jump. The background graphics and variety make it much more interesting.
So it seems that sometimes you just walk up some stairs or do a single jump, at other times you have to jump from side to side, or sometimes from sides to center blocks, or even have to jump through one-way blocks. The best places (in my opinion) are a crazy mix of each. This is probably much easier to automate if your screen can be split into an even number of floors like the last image; that way you could place the floors and then pick random ways to move between them. It's also good to point out that each region has it's preferred method for going up. Don't forget to carefully plan the architecture to match the height and jump hight of the main character.
This may have been pretty obvious to most of you, but I learned a lot: you can use the same action (jump to the upper left then the upper right then the upper left....) but provide slight differences in art and layout and it will still provide interesting architecture and opportunities for fun. I've also got some working code to create rooms with layouts like the last image. And lastly; after 15 years, C:SOTN is still a beautiful and intricate game.