The pipe glitch only works in v1.0. This includes dying inside the pipe, and pausing and quitting while inside the pipe. However, pausing and quitting while touching an object (mushroom, starman, bubble item, bell...) to carry those items into another level works on all versions.
Aside from pipe glitching, there are various other ways to enter the out-of-bounds area:
1.)
Sprite-spawning glitch. Have an enemy that spawns objects (chibi dracula, fire-spitting piranha plant, pig) stand offscreen for a long time. They will spawn their stuff until all the object slots are used up. When having everything appear onscreen now, the game will glitch around - You can zip vertically through the ground by jumping, but this only seems to work with floaty state (address A287 controls this), so when you are in moon zone 1 or have the bubble item acquired.
2.)
Tree Zone 3 (right). In this level you can go out of bounds by reaching the place above Mario, in the beginning of the stage, using the bubble item to fly up or a bee enemy to jump on.
3.)
Pause glitch. When the game lags and you are pausing, the game may reset itself or place solid/breakable blocks somewhere on the screen randomly. Theoretically you could set up a spot of blocks that you can slide into, and get ejected into the out of bounds area. This is only theory, but maybe I'm gonna prove it someday.
4.) --- maybe there are more ways, but I can't recall them...
