I'm guessing the marketing team had no idea that Kelsey wasn't going to return. Which is why they didn't list his final performance. I'm guessing for whatever reason Kelsey decided to leave either before his contract was up, or he had a clause in it that allowed him to leave early.
I think it's perhaps a bit premature and unfair to blame them if they didn't know. It seems that it was even unclear when exactly he was going to leave. Whether that had to do with Kelsey and his schedule or getting Warlow up to speed is hard to say.
Obviously Kelsey changed his mind about continuing in this show. Could be personal or could be that he didn't want to continue in the show without the Tony/review accolades. Perhaps he had other opportunities and he felt that FN gave him all it could.