Sifting through the ashes

While I wait to see how my novel about William Marshal - The Greatest Knight is performing in paperback in the bookshops, I have continued to work on the story of the above's father, John Marshal. Working on the research is proving both fascinating and frustrating as witnessed by my attempts to get the facts about the Wherwell Abbey incident straight.
The incident goes like this - roughly. John Marshal and his troop were fighting for the Empress Matilda in the war with King Stephen for the English crown. They had to guard a crossing of the river Test at Wherwell and were faced with the larger, stronger troop of mercenary captain William D'Ypres descending on them from Andover, which D'Ypres had just sacked and burned.
The two forces fought a running battle and John and his men were finally driven into the Abbey. D'Ypres set fire to it and John was burned, losing the sight of one eye.
So now I come to write this incident and find that no one report agrees with another. I have around five different versions of the same story plus other snippets garnered here and there. Sure, there are similarities, but getting at the truth is like picking up individual grains of rice wearing thick woolly gloves.
What was John doing at Wherwell in the first place? One chronicle says the Empress' forces had built a temporary castle there as a forward base and to guard supplies. Feasible, since John was the Empress' marshal and responsible for various aspects of quarter mastering. Others make no mention of such defences. Sometimes the nuns were there and squawking about what was happening to their convent, at other times they aren't mentioned. What's the reality? Anyone's guess. Two reports say that John Marshal lost an eye during the burning of the Abbey and since one is the epic poem L'Histoire de Guillaume le Mareschal, it's likely to be true. But other aspects of the Histoire fudge the truth in the interests of a good story. John it says, was responsible for getting the Empress out of Winchester and for telling her to ride astride like a man. However, he wasn't anywhere near her desperate flight from the city, but was guarding that all important ford at Wherwell. Had he rushed there or was he there already dealing with supplies and surprised by the forces of William D'Ypres? What happened to the knights who were with him at Wherwell. Geoffrey Boterel was the brother of the Earl of Richmond and he didn't die there. 1148 is his given death date. What happened to Richard of Okehampton? Were they captured and led away in thongs (!) as one chronicle says. Did John really hide in the tower while the roof burned over his head, or did he make a break for it?
What I have to do with the information from all these disparate reports, plus some valuable remote viewing notes of the incident and an afternoon spend walking the ground myself, is write a credible version of the scene. I'm enjoying the challenge, but it goes to show that Pontius Pilate was right when he said 'What is truth?'

Photo is of the River Test at Wherwell. No trace of the abbey remains