When verifying the French translation against the English text (or vice versa), we often find errors in the English. This can happen even if the English had been edited before going to translation. There are 2 main reasons:

The English text may be ambiguous enough to lend itself to more than one interpretation. This can occur even in text that is grammatically correct.

If the translator is not also a content expert and may not be aware of certain concepts — particularly if they are new or heavy with jargon.

To keep the process efficient for everyone, don’t send the English to the designer, printer or Webmaster until the concordance is done and any errors corrected.

This means that when planning the overall process, take care to give the translation phase enough of a turnaround time to adjust the translated and the original versions.