One thing that I will never forget about my experience with European patent oppositions is that to American eyes, the European process appears to be rather “due process of law” impaired.
For example, although in theory, issues should be argued in advance by written briefs, the European opposition process also allows parties to introduce new issues during the last minute oral arguments.
This allows for litigation by “unfair surprise”, rather than by reasoned arguments. In this sort of setting, I have seen that illogical but last minute “Chewbacca defenses” can work quite well. The clock is ticking, proceedings are going to finish in an hour, and suddenly you have to discuss entirely new and logically irrelevant issues. It is as if you suddenly have to shift gears and focus on if the Star Wars character Chewbacca lives on the planet Endor or not.
In this regard, it is refreshing to see that the Federal Circuit in Dell Inc., v. Acceleron, LLC (March 15, 2016) has confirmed that this sort of litigation by unfair surprise is unacceptable for US PTAB patent reviews. Due process wins — arguments made during oral argument must be restricted to only those arguments previously discussed in writing beforehand.