Forum:KB:Question about General Grievous

The Clone Wars (the 2004 version) clearly shows us that Grievous' breathing problems began when Windu tore his ribs apart while he was kidnapping Palpatine. However, in the 2008 Clone Wars series, which in chronological terms takes place before the Battle of Coruscant, Grievous already presents those breathing problems. Why is that so? Is there a logical explanation, or is it a mistake on the part of Dave Filoni?