What actually happened at the Fist of the First Men?

I always found this part (straddlin S2 and S3) confusingly portrayed.

At the end of S2, through the eyes of Sam who has been separated from the group, we see the Army of the Dead (or part of it) marching.

In S3 it is clear that the rest of the Nights Watch ranging group engaged them in battle. While many were killed, many also survive including every 'named' character.

So what happened? We saw at least 2 White Walkers in the group in S2. Were they killed? They had no Valyrian steel (whoops Mormont), although they had just found the Dragon glass. Nonetheless when Sam later kills a Walker it seems to be clear he is the first to do so.

So did they somehow escape? If so how!?

I wonder if it is clearer in the books. The battle is of course not shown on the show (presume Blackwater had taken all that budget).

Any thoughts appreciated!