Geoclue got started during GNOME Summit 2006 in Boston. At least Keith Preston and Tuomas Kuosmanen can be blamed.
There was a total rewrite after version 0.9. Use tag "0.9" (as in git checkout 0.9) if you need the old code.
There was yet another rewrite that we call geoclue2. The first version to introduce the re-write was 1.99. You can find the rationale for the re-write here but I was way too lazy/busy to preserve the previous wiki page.