Some owners, like Cargolux and Delta get involved quite early on in the pre-delivery process, I know Delta have had probs with some of their aircraft so they have in the past sent engineers/crew out 6 weeks prior to scheduled handover to work with Boeing.
My Ex used to work for Cargolux and he was saying they had so many probs with their last 747 that when their next one was delivered they were going to send an engineer out for the last 3 months if it's build and flt crew out for last 6 weeks
Sounds odd but it happens