The slicks had been done for months, Derek knew about them. He was also frequently attending their sessions. Either Derek was making it up to buy time or Brian told Derek something to buy time, I don't think there's much to this. Still interesting.
Very interesting - the goings on between the various members of the group and Capitol execs or whoever in putting an end to SMiLE are endlessly fascinating. One day someone's gonna find those finished tapes and we'll all be left with nothing to speculate about!