The editor of this edition, Jay L. Halio, has made the decision to base the text purely on Shakespeare's folio, rather than on the more usual conflation of the folio and the quarto. Quarto passages which aren't in the folio appear in an appendix at the back. This means that the text in this edition departs quite significantly from the text of other editions in key places. Halio makes a scholarly case for his decision representing something closer to Shakespeare's final version of the play, but it's frustrating if you're interested in the quarto or if you want to read King Lear in its more usual modern form.