When you search FAQs for "edit comments", the only thing you find is FAQ 189 on "irreparable markup", which tells you that "you cannot edit comments".
That hasn't been true for quite a while, so the sentence in parentheses should probably read something more along the lines of "If the error is in a comment, you can edit it only if you have a Paid or Permanent Account and nobody has yet replied to the comment" with a link to FAQ 15 and then perhaps the existing "you will have to delete and re-post the corrected version", though you'd only want one link to FAQ 15, not two.
Also, the list of Paid Account benefits could stand to add "the ability to edit comments" somewhere in the list of features for personal Paid Accounts.