Face won't recognize an edge

My first real Blender project has run into a few issues. After screwing up the geometry of my wyvern’s crest, I tried to fix it by adding in an edge and turning the shape back into a cube(ish) thing. It didn’t work, because as you can see here, the face does not recognize the new edge. Any ideas on how I can get this resolved? Thanks in advance!

delete the face select the edges you want to be the new face and hit “f” to create a new face there.

That kind of issue can come from filling a edge/face (hotkey F) for vertices that already have a face. Would have to connect/join (J key) them instead.

If you have a lot of those, could also use a new tool in 2.72 to split those faces:

Split by edges is in faces menu (hotkey ctrl+F).

Sorry for taking so long to get back on this, it’s been a busy week. Anyway, I ended up just redoing the crest, but for future reference, without extruding, how do I add new faces/edges that a loop cut will still recognize? F, or J? Or should I just loop cut?