It can be found in the preface of Le Petit Prince, Éditions Gallimard 1999, in the third to last paragraph, and I haven't found a sufficient translation online. The complete sentence is:
et bien des détails s'en sont trouvés ainsi altérés, voire mis à mal.
Here is an explanation.
Malmener, détruire ou mettre dans une position difficile quelqu'un ou quelque chose.
It is not very precise. However, as what precedes tells you that some of the details were individually partly changed (altérés) and that the word "voire" tells you that what is considered next is of greater consequence, you can surmise that something worse than a change was the conclusion for some of the details and that could go as far as some of them having been entirely discarded, or reckoned with, for instance, as almost complete lies.
