For example, Capo Ferro is superior to Bonetti, but is cancelled out by Thibault ; Agrippa is superior to Thibault, but is inferior to Destreza, etc. Therefore, your character gains a +1 bonus when using Thibault against a Capo Ferro swordsman, but will lose this bonus if your opponent switches to a different fencing style. And if your opponent has studied his Agrippa, he could turn the tables on you and gain a +1 Fencing bonus against your character.
Revelations of Mars, Fencing Styles
Voilà une explication qui m’a particulièrement parlé.