I hope some forum members who have seen relevant ULTRA material will comment here. I would pin some hope on Signatur RL 10/65 at Freiburg. Has anyone seen that?
Not a year I've ever looked at but anyone who wants to try can view the material via the National Archives website. DEFE3/185, German Naval messages deciphered 5–10 August 1942, and /186 (10–16 August) might be a good place to start.