Banger - Chart Cold-Boxes are used in many cryogenic processes including LNG and Hydrogen. LINDE, Air Liquide, and Air Products have been using Chart Cold Boxes for decades, so a PLUG reference is not necessary.
As for PLUG's Joule Liquification Process, Chart Cold Boxes are still an essential component . I strongly suspect that the Chart Cold Boxes were NOT the hold up, but instead it was with PLUG's serial # 1 Liquefier.