A couple of ways that source code can lie: 1) Wrong code revision: The source you're looking at is from version 3.00, but you're actually running on version 3.14.159.This mostly happens when you used pre-compiled binaries instead of building the application/library yourself. Or because you Googled for the relevant source keyword instead of searching through your own local source files. 2) Wrong file(s): You *think* that you're looking at the right code, but it turns out that it's an unused copy or variant that isn't actually what's compiled into the library you're using. This often happens when you're dealing with code that's meant to be compiled for multiple targets, eg. Linux kernels and drivers. Other times it happens because a file was moved or replaced, and the old version was left lingering in the repository.