I book KL upgrades to Africa around once a quarter. Once in about every five agents do I get one that knows how a GUC is applied, what the terms are and what needs to be done for it to take with KL. In fact for this most recent trip, it wasn't until the morning of departure on the outbound I realized the agent had incorrectly booked and gave me Z-class space on the return, which when reissued, ended up being the continuation of my outbound flight back to AMS. Luckily they were able to fix, but moral of the story is HUCA, HUCA, HUCA. Then check their work like a fox.