I don't think that this is concrete evidence that he only attended one rehearsal. It's not like Sebastian was at all of them, and there is no direct quote in the article. I wouldn't worry about the older songs - he wrote those songs and has been playing them for a long time. The new stuff - well, we'll see how much they play.
For the person who said he's not 28 anymore and therefore needs more practice, there is a possibility that people become better musicians as they get older instead of worse. It would be nice to think experience and wisdom count for something.
Best post in the whole thread; those last few sentences have a great point.