AFAIK sometimes they can form wrong(specially in modded) or not at all. But there are always 3 of them in any world and since you now know the location of one you can easily find the other 2. I believe they are placed on the points of an equal-distant triangle centred around spawn.I'm having a buit of trouble on Infinity (I believe I generated the world as 1.10, and it is updated to 1.11.2) finding a Stronghold. I kep tossing Eyes of Ender until they led me to th top of a cliff, where they just hovered. I picked up my TC hammer and dug away don to bedrock... Huh...
I turned on my jetpack and threw a few more, as I noticed they were flying away from bedrock, up to about level 45. I started digging sideways, everwhere. Went into some caves (the big ones, with ravines and whatnot) aaaaaand, I got nothing.
what am I missing?
EDIT:
There is a limit of three strongholds per world (1 per world in console versions). All strongholds are located at random positions in a radius between 640 and 1152 blocks from the point at x = 0, z = 0 (not the world spawn, which may be a couple hundred blocks away. Strongholds also may extend further in or out of that area). The three strongholds are spawned at roughly equal angles from the center point of the world (that is, each stronghold is in the region of 120 degrees from the others, measured from the origin).