On minecraft is the same seed number different each time you enter them because the description of seeds that other people have posted dont match the world I create when I enter it?

Answer 1

The seeds are version specific, as more things are added to minecraft, like new wood types, new biomes, the seeds do different things.

So while a certain seed would always give the same thing on v1.2.5, it would give something different on v1.3.1.