marshalGreg
I assume you are referring to Silborne's mention of the French Dragoons at Quatre Bras on page 94?
If so, I think sadly, that Silborne's mention of the dragoons only adds to the confusion concerning the dragoons actually being there or in action.
The reason for this is that while he states 'Whilst that portion of Kellermann's dragoons which had dispersed the 69th regiment….' (page 94), if you read his description of the cavalry attack against the 69th Regt on the previous page, there is no mention of dragoons taking part at all. Instead, he describes the British regiment being attacked and rolled up by Cuirassiers who also captured their colour. And further down the page he describes the 30th Regiment driving off Lancers and Cuirassiers, but again, no mention of dragoons.
That is not to say that French dragoons did not take part or were present, but had they been engaged in the action against the 69th, as he suggests on page 94, then you would have expected him to have mentioned them in the actual attack on page 93, if indeed, they did take part?
As to the reliability of the author, by mentioning the dragoons being present, correct or not, I don't think it would affect the reliability of his work overall.