I'm watching a UK Customs programme. They use drugs dogs on incoming packages because the dogs speed up searching mucho.
Doggie #1 alerts to two packages. Don't ask me why but the Customs Officers are obliged to get permission to open the packages.
While they wait ...
They trot up doggie #2, who also picks out the suspect packages.
Then doggie #3, who alerts, and doggie #4, who also alerts.
Doggies 2-4 were considered to be on training, as the Officers had as then not been given permission to open the packages. What had they been training on?
Then permission was given to proceed.
The shipment was books wrapped in cling film. When opened, the books were hollowed out, and under a fairly simple blocker were packets of cocaine.
Total street value in excess of £1 million
That's 4 smart doggies, all for a reward of playing 'fetch' with a tennis ball.
And doggies 2-4 were training on cocaine. 
Therefore the alert made by dog #1 whose name we do not know, was corroborated by three others trained and training in the same discipline and the contraband was subsequently found and recovered.
The alerts made by Eddie were not corroborated by other cadaver dogs ... although the CSI dog trained only to alert to blood alerted to the car key fob and at the couch in 5A as Eddie did; nor was any contraband in the form of human remains recovered.
The contraband was proof of the intelligence supplied by the drug dogs; there was no forensic proof for the intelligence supplied by Eddie.