Good point, it doesn't sound like a furtive rendezvous. I've long wondered how all the various car movements around 37SR were handled if the abduction began there. Somehow SJL and Mr Kipper both went there, he in his canonical BMW, so what happened next? They drove in her car - OK so when does he retrieve his? They drove off in his car - OK so how does hers get to 123SR? In neither case is an abductor going back to 37SR to collect a car, given that by this time it's possible she's been missed.
One possibility that works (and fits Cannan) is if he actually arrived on foot - in Cannan's case, from
his mate's flat in Star Road 10 minutes away. It would explain the BW sighting in that he gets her to drive him around, including to wherever he has left his own car.
Another conjectural fit with Cannan may be something that happened with SB. When SJL disappeared it was a major story in less than 24 hours, which would have significantly constrained a kidnapper. If this were Cannan, did he conclude that next time he needed to keep the heat off longer, and thus contrive the call to the office by SB?