The statute of limitations has a lot of loop holes. For instance conspiracy statute of limitations ends with the final act of the conspiracy. -
>The rule for conspiracy is a bit different. The general conspiracy statute consists of two elements: (1) an agreement to commit a federal crime or to defraud the United States and (2) an overt act committed in furtherance of the agreement. Conspirators left uninterrupted will frequently continue on through several overt acts to the ultimate commission of the underlying substantive offenses which are the objectives of their plots.
>good thing the sealed indictments were filed LONG AGO.
And there's this too.
A sealed indictment can "prolong" the statute of limitations time frame.
>The statute of limitations runs until an indictment or information is found and returned to the court.54 There is, however, some question about the impact of sealing the indictment upon its return. The Federal Rules of Criminal Procedure allow the magistrate to whom the indictment is returned to seal it until the defendant is apprehended or released on bail.
Lastly, there is no statute of limitations on treason.
Sauce: https://sgp.fas.org/crs/misc/RL31253.pdf