How much time are you talking about? If there is no interest indicated by the dog, there is no interest.Are you saying all other 6 residences must have had cadaverscent contaminant from dead (or live humans as it put across ) but Eddie wasnt given the chance to find it?
IMO mercury - the car video is the best example of the difference in timing. The most time spent at any of the other cars was 30 seconds (and that's being generous). Eddie did not even do a full circuit of one of the cars before being allowed to move on.
So - after 30 seconds no alert was made. But that is no different to the Renault - as no alert had been made to it after 30 seconds either. The difference is that - unlike with the other cars - Eddie was not allowed to move on from the Renault - he was called back numerous times - with MG actually tapping the car in places - and it was 2 minutes before he alerted.
If Eddie had been directed to spend the same amount of time on the other cars - then (unless you believe no 'alertable material' had ever been deposited in any of those cars since their manufacture) - alerts may well have resulted. But he wasn't - so we shall never know.
The same principle applies re the apartments.
AIMO