IIRC, for Japanese people, even Teineigo is part of Keigo.
In learners' resources (where Teineigo is introduced usually right at the start), my impression is that Teineigo is not included, and that Keigo starts with Sonkeigo and Kenjougo. That's still introduced comparatively early, but much later than Teineigo (I think, it's in Genki 2, for example).
To me, this is the part that is keigo. The other stuff is relatively simple and early in terms of language acquisition.
Assuming that others share my definition of keigo may be assuming to much on my part.