I don’t know about wrong results, but compare Godement’s *Algèbre* ([1966](//books.google.com/books?id=pW9GAAAAYAAJ&q=%22classe+à+droite%22), and still 1980):

> on dit que l’ensemble $x\mathrm H$ est une **classe à droite modulo** $\mathrm H$  

(translation: “we say that the set $x \mathrm{H}$ is a **right class modulo $\mathrm{H}$**”)

with everyone else, e.g. his associate Bourbaki ([1970](//books.google.com/books?id=4RIDPH1ULXcC&pg=SA1-PA33&dq=%22classes+à+gauche%22)):

> les ensembles $x\mathrm H$, qu'on appelle ***classes à gauche suivant*** $\,\mathrm H$ (ou ***modulo*** $\,\mathrm H$)  

(translation: “the sets $x \mathrm{H}$, which are called ***left classes following $\mathrm{H}$*** (or ***modulo $\mathrm{H}$***)”)