Yeah, the burn patterns are not linked to the sticking issues in any too direct way, I understand. The sticking mostly comes from the Lycoming's design running the stem area hotter than the design can do, it appears, and the QC I'd argue. A perfectly seating valve face can stick very well. I'm hardly knowledgeable in this area, as I've studied it very little because we had no this kind of issues around here in the engines I followed.
Any asymmetrical burn pattern on the face, such as:
..gives an indication of a valve
face failure, or of a poor sealing on some edge (the latter often giving a result of the former). Albeit this specific example appears to have some evidence of detonation as well, maybe having caused the valve failure in the first place, but regardless!
-Esa