The America Invents Act (AIA). Here's a good article that explains it: http://www.sgrlaw.com/resources/trust_the_leaders/leaders_issues/ttl31/1779/

"Misjoinder of Defendants

With the enactment of the AIA, simply infringing the same patent is not enough to be co-defendants in a single suit. Accused infringers can now only be joined in a single action for patent infringement if the right to relief arises out of the same transaction, occurrence or series of transactions or occurrences relating to the infringement, and the right is based on common questions of fact. "

Read the entire article for good background. The AIA was fully implemented by March 16, 2013.

So yes, Agility may only file cases one at a time aginst potential infringers, if each assumed infringer balks at Agility's recommended license fee structure. At the end of the misjoinder section linked above, a plaintill filed 38 separate cases.

"The recent actions of Beacon Navigation GmbH are in complete contrast to those of Optimum Power Solutions, but could be a precursor of things to come. On October 11, 2011, Beacon filed separate patent infringement suits in the U.S. District Court of Delaware against 19 defendants that Beacon alleged had infringed each of two patents, for a total of 38 different lawsuits."