Unfortunately, the two accounts differ in many ways: the parties involved, the number of combats, and the outcomes of many of the combats. Perhaps it is best to start with where their accounts agree.
The English and French agreed to fight a number of single combats at Vannes. Each combat would be for a set number of blows on foot with different weapons, which included spear, axe and sword. Based on similar combats, this meant that when one or the other champion has struck the set number of blows, either five or three depending on which account you accept, that phase of the combat was completed and they would pick up the next set of weapons. The combat could end early if one of the champions was injured or overmatched and the judges intervened. However, at least one Englishman offered to complete the full number of blows for a companion who was unable to continue, and had his offer accepted.
Each contest began with lance on foot. Froissart describes the champions going at each other at "a good pace" and putting their lances to their breasts. Cabaret also describes the contestants "coming strongly against each other" in a way that seems similar to a later lance combat.
In the first combat one of the champions was wounded in the body by his opponent's spear in spite of the plate defenses he wore.
In the third combat Clarins or Glarains, a bastard of Savoy, struck his opponent, Edward Beauchamp, to the ground twice with his spear.
Then came the last, Edward Beauchamp and Clarins de Savoye. This bastard was a tough and brave squire, and as well formed in all his limbs as the Englishman was not. They ran at each other with a hearty good will: both set their spears on their breast in pushing; so that Edward was struck down and backwards, which angered the English greatly. When he was raised up, he took his spear and went against Clarins and Clarins against him, but the Savoyard again struck him to the ground, which made the English very angry: they said, Edward is too weak against this squire, and the devil was in him to joust against the Savorard. He was carried off among them, and said he would not fight no more.*
In the final encounter, Jean de Chateaumorand fought William Faringdon, who wounded him clear through the thigh in violation of the agreed rules for the encounter. The English were enraged by their own champion's misbehavior and made strenuous apologies and other efforts to make amends, which were ultimately accepted by the French.
Who to trust where the accounts differ? Froissart had an attitude more like a docudrama writer than a modern historian. He strove to create a vivid account of events, and if he didn't know all the details he supplied plausible ones of his own invention. We have no reason to think he was present at Vannes.
Cabaret d'Orville had a well placed source, Jean de Chateaumorand, but hardly an unbiased one. And he was writing about forty years after the encounter, while Froissart was writing when memories were fresher.
For some details, Cabaret is simply more plausible. He says that the victim in the first combat was wounded "between the lames and the piece" It seems likely that the piece in this case was the breastplate, the largest piece of the body armor. The articulation between it and the lames that covered the belly would be a relatively weak point in the body armor. Froissart says the breastplate itself was pierced, a much more challenging task.
Cabaret says that in the final contest, there was a special concession. Faringdon had a knee injury that prevented him from wearing armor, and asked that both champions fight without legharness, and that neither would strike at the other's legs. This makes the serious wound that Chateaumorand suffered more plausible: such a wound would be much less likely if legharness was worn. Froissart seems to have heard about the legs being off limit in that fight, and mistaken a specific accomodation for a general rule.
Froissart seemed to think the arms were off limit as well, but this, if true, would be a unique restriction for foot combats in this era. Cabaret, on the other hand, says that one of the English was wounded by a sword stroke that broke the mail between the piece and garde bras** and pierced his shoulder so that the fight was halted, another by a lance stroke that pierced his arm between avant-bras* and garde bras*. In neither case was this seen as a foul blow.
Froissart says there were three blows with each weapon, Cabaret five. In this case Cabaret seems more plausible. Three is a relatively low number of blows for a combat on foot: a contest planned in 1400 expected ten blows with each weapon. Three is exactly the number of blows per weapon specified for a mounted combat that Froissart says he witnessed in person, but the smaller number would be more appropriate to contests that included the particularly dangerous courses with sharp lances on horseback.
Cabaret adds that the planned exchanges would also include strokes with dagger, a common feature of such contests around this time, if the fights lasted that long, but that none did.
In all these things Cabaret seems to provide the more plausible account. However, in another dimension his account seems more dubious. In his version, the French are uniformly more generous, competent and victorious than the English, decisively winning every fight before Faringdon's foul blow. In addition to the combats already described, Cabaret also says that Tristan de la Jaille badly wounded his opponent with his second axe stroke, so that he could do no more. In Froissart's version the honors are more evenly distributed. Chateaumorand was both a principal and a partisan in the events described. Is it possible that he forgot, misremembered or shaded some details of a combat forty years in the past that might have been less flattering to his team? Is it probable that the French put so many fully armed opponents out of action in so few blows?
Whoever we believe, at least the two sources agree on many of the details of the deed of arms. Fought on foot with several opponents and a variety of weapons, it provides a valuable prototype for those interested in creating the foot combats of this period.
*Froissart, Jean, 1867-1877 Oeuvres ed. Kervyn de Lettenhove, Brussels Vol. 9 pp. 326-327 Translation copyright Will McLean 2012
**Garde bras: upper portion of armharness. Avant-bras: lower portion of armharness, cognate with vambrace