Yes, it's true. Ever since the blueprints update went live at the end of March of this year, very rare vehicles that have been in different events can be much easier to obtain. Some have a certain amount of blueprints, with either Common, Rare, or Legendary exclusivity. Blueprints are available in any box there is. They can even appear within the three Fusion System boxes! Some are found in events, R&Ds, Enduro Double Downs, Championships, and in the Moto Blitz seasons (Lamborghini Huracan)!