Remember FISA = Federal Intelligence Surveillance Court. It isn't law enforcement, so FISA warrants have much greater latitude to collect than a law enforcement warrant.  My understanding is that if you leapfrog under FISA, the collection is expanded and captured but cannot be accessed until FISA givens the nod to expand - but the collection is already complete.  Under LE courts, if a pedo or drug dealer is on surveillance which captures another party.  That party's communications are inadmissible in court until a judge grants an expansion of the warrant.  There should be no prior collections before the warrant. That being said - The FISA warrant which allows chain collection effectively means the collecting agency (usually NSA) could in theory, collect on everyone.  There are only about 4 degrees of separation, maybe 3, between everyone in the US.    Search for "verizon FISA authorization".  All of the information is in that recently leaked document.