Why does virtually every source agree that Richard Plantagenet, Duke of York's claim to the crown was stronger than Henry VI's? Usurpation by his grandfather aside, Henry VI was descended from Edward III's third son, John of Gaunt, while the Yorkist line was derived from Edward III's fourth son, Edmund of Langley.
There was also a female line descent from the second son. It was the lack of something like a salic law in England that complicated things over whether a senior cognatic link beat a lesser agnatic link