Leahy-Smith America Invents Act, makes it tougher to join parties to existing law suits, relative to rule 18, 19 or 20 FRCP, because Plaintiffs are failing to meet the tough requirement of same transaction or occurrences. In this scenario, if a Plaintiff have John Does, is it easier to add John John Defendants, if you have newly discovered evidence they are liable to the infringing acts? Also Judges are more likely to dismiss case for improper misjoinder, then adding the true name of your John Does.
This question is relative to infringement cases, of adding new parties or the true names of John Does.
Judges are usually more lenient with amendments such as this because it avoids having to do the case all over again or have separate lawsuits. That said, federal judges are ALWAYS looking for ways to get cases kicked out of their courts.