There are many types of errors possible.
One is the "transcript" of what Martin Grim is alleged to have said regarding putting Eddie in the car...
Whoever translated that (and this preceded the volunteers once the files had been released) who I presume must have been someone connected to the PJ team at the time... got it... erm, wrong.
The volunteers correctly translated, according to the PJ's translated transcription of what MG said, that Eddie was going to be deployed in the boot.
The fact is - MG said exactly the opposite. There is no evidence that Eddie was ever deployed in the boot. Tavares de Almeida / Amaral then appear to have copied this incorrect translation including the omission of a potentially innocent missing "não" from the translated transcript to the infamous interim report... and, hey presto, Eddie magically appears to have reacted to cadaver odour in the boot.
Such errors can occur, but wouldn't leading investigators have checked whether the footage of which dog was put in the car corresponded to the translated transcript? This was, after all, supposed to be the smoking gun.