Are you suggesting that dessicated blood would have been found in the other apartments if only they had given Eddie more time in them? I think the scent is either there or it isn't, time isn't the issue.
Eddie was very interested and eager in 6A. He very quickly alerted in the main bedroom. Once he had done that a thorough inspection was needed. He then alerts behind the sofa. Keela is used next, and she also alerts behind the sofa.
Eddie was taken into the other apartments but he showed none of the eagerness or interest that he showed in 5A, so Keela wasn't used.
According to Grime both dogs could detect blood deposited decades ago - even if it was in such minute quantities that it could not be detected by the human eye or by forensic examination.
Anyone who believes that none of the thousands upon thousands of people who had spent their hols in those apartments over so many years had ever shed a single drop of blood in them needs a reality check IMO
Incidentally, sniffer dogs would not be constantly alerting - as they are not permanently on duty. They go to work (or play as they see it ) only when commanded to by their owners - the rest of the time they behave like any other dogs.
IIRC Neither of the dogs made immediate alerts - they both spent some time searching around before they did alert.
The difference in the amount of time spent in searching anything McCann-related - compared to everything searched that was not McCann-related is undeniable - and is proved by the videos. E.G. 30 secs or less spent on all the other cars. A full 2 minutes spent on the clearly identifiable McCann car.
As I totally believe Grime's claim about his dogs ability to detect very old tiny residues - then the reason why they did not alert in the other apartments and the other cars
can only be time-related IMO. I do not believe it was because there had never been any blood there in the first place as that is simply not possible. IMO.
AIMHO