The location of the 200+ Nigerian girls was not known. But the CLAIM that that location was known elicited 'chatter' from the kidnappers, the location of which was then triangulated. Cool. The mere use of publicized speech did the trick, not physical sleuthing nor tracking.
Unfortunately while the Nigerian army is good at burning down Hausa villages, it is not able to do a surgical operation. And most of the girls have been married off or ransomed by now anyway.