The dog handler knew from initial responses or in most cases the lack of them whether it was worth pursuing other objects.
M. Grime tells us that
1. Eddie and Keela alerted to blood from living persons.
2. that they alert to deposits so small that they cannot even be detected by forensics.
3. that they can detect blood deposited decades ago.
I do not believe that with the huge amount of holiday-makers (families) who stayed in those other apartments over the decades - that at no time had anyone ever spilt a single drop of blood in them.
With regard to the cars. Eddie showed as little initial interest in the Renault as he did in the other cars. It was not
his behaviour which changed around that car - it was Martin Grimes. It took a full two minutes before Eddie finally alerted - but only after being repeatedly called back - with MG even tapping on the car to draw the dog's attention to it.
The maximum amount of time spent on any of the other cars was 30 seconds, in fact Eddie did not even complete a full circuit of one car before being allowed to run off to the next one.
If Eddie had been made to inspect the other cars for a full two minutes - then IMO there would have similar alerts in at least some of those cars as with the Renault.
In any event - the fact that the Renault was clearly identifiable as belonging to the McCanns meant that any claim made that the testing was unbiased was completely untenable.
AIMHO