Source of features on 1844 GLO plat?

Continuing my study of the Chief Black Hawk story, I'm puzzled by the fact that I don't find in the transcribed GLO field notes any mention of some of the things depicted on the plat, for instance a house and the (mistaken) bluff.

Would there have been notations or sketches in the original field book that were platted in the office but not transcribed into the office books or mentioned in the WPA typescript? How else would they have gotten on the plat?