Blancpain

       I am looking at acquiring an aqualung grande date through a private seller and I have two questions, I would be extremely grateful if any existing or previous owner may provide some information. First, does this watch have a screw-down crown or is it a push-pull type? Second, does anybody know if Blancpain maintain a registry of stolen watches? if possible I would like to check the serial no. and confirm the watch wasn't stolen before as unfortunately the current owner no longer has the boxes/papers. Thanks in advance.

Best Regards,

Phil