WMG for Wyrd Sisters. Warning: Potential unmarked spoilers.
The last name of Hwel, the dwarf playwright from Wyrd Sisters...
Verence II was the bastard son of the Queen of Lancre.
Because of the way it had been implied that the young Gytha Ogg "committed treason with a leg of mutton" (assuming "his life above stairs" was an Unusual Euphemism, and not literal). The Land accepts him because he acts properly kingly, rather than like a gluttonous, mad, or otherwise unfit usurper.
- Is it still Wild Mass Guessing when it's stated outright?
- It's stated that Verence II and Tomjon were the sons of the former Fool, who was a very good climber and "very popular at court". Also if you notice, neither man was able to see the ghost of Verence I, which could only be seen by wizards, witches, and relatives.
The History Monks are aware of Granny's use of a Timey-Wimey Ball but have not intervened.
As pointed out in the main section, the Discworld timeline is a bit dodgy. To answer the question whether the History Monks had to fix up these events in any capacity, perhaps they did notice, but thought that everything has turned out as it ought to be (for a given value of 'ought to'). That gives them a spare fifteen years that nobody was using, which might be useful somewhere (or somewhen) else. Besides, the Monks know an immovable object when they see one, and wouldn't be game to confront Granny directly.