This whole plane was an afterthought and thus it turned up not being subdivided properly. Now I want to manually subdivide into just grid according to vertical and horizontal vertice pairs. Basically to make all top vertices connect to corresponding bottom vertices, and the same for vertices on left and right. Knifing this manually is bothersome. Any ideas?
I fucking did it using "connect vertex path (J)" and a bit of smart mirroring/vertex merge, much much more faster than knifing, but still a bit grindy. So if you know better ways please tell.