SL2 is relatively straightforward, but SL1 & 3, and SB1 & 2 are probably the hardest levels in the game to max out, and require a lot of work. They're a lot different to other levels where you can just go through and collect all the rings.
And yes it's true that of those levels you can only get ALL the rings on SB1, but it's really hard to work out how, and possibly even harder to achieve it once you've worked it out