Thankfully fergies kids are down that list. I do like fergie more then Diana but her kids seem strange.
Trying to think of a time besides 1377 that the normal succession bypassed birth order. At that time the Prince of Wales had died incumbent (in battle), and that title and the succession fell to his son.
Other hiccups in succession were the result of various kinds of civil war (Wars of the Roses and the Stuart/Cromwell events for instance).
Even in 1938 the Prince of Wales succeeded to the throne upon the death of George V. He abdicated before hs coronation, but unlike American inaugurations, the office passes immediately on the demise of the crown. The coronation plans were in being, they just had to change the name for George VI and include a lesser throne for Elizabeth the Queen Consort (known to us as the late Queen Mother).