I'm always amazed by Gold+ medallions who never get C+ seats. I've been FO for two years, and have near 100% success getting C+ window or aisle when traveling alone. If I'm traveling with a companion, it's harder, but still at least 75% success. Just be prepared to check the seat map right at T-24 (or T-72 for GM). If I don't get C+ then, I start check the app periodically - C+ seats open up as people SDC. At worst, ask the GA if s/he can move you to a C+ seat as s/he processed upgrades.