Erica, thanks for making that point. When I first came to this discussion, I dismissed the idea that the Breretons could be descended from Ada exactly because there was no Brereton Competitor.
Then we saw the monumental inscription that explicitly says the wife of Ralph Brereton was Ada, daughter of David, but there are reasons to believe the inscription is late and perhaps from a reconstructed tomb. Now Lloyd adds that in 1576 the inscription was noticed as being in characters more modern than the rest of the monument (Doug Richardson citing Omerod).
Then we saw the coat of arms, also very late, of a Brereton man quartering a le Scot heiress. When I was writing about it I didn't think of this specific problem. If the Breretons were entitled to that quartering, that would put one of them back among the Competitors, wouldn't it?
Or maybe not. I've seen many simplified genealogy charts that show the relationships among the Competitors. All of them eliminate the siblings in order to focus on the actual 1291 claimants. In other words, junior members of the family are ignored, as indeed they must have been at the time.
Perhaps the same applied to cousins. if John Hastings was the senior descendant and represented the line of Ada, perhaps a cousin with junior rights would have been disregarded as a Competitor.
I'm leaving open the possibility, but I don't accept it. Everything I'm seeing suggests the 16th century Breretons believed they were descended from Ada, daughter of David 300 years earlier, but their belief doesn't prove they were correct.
I think the answer to this puzzle is going to be something else. Maybe Ralph Brereton married a different woman in the same family (who might or might not have been an heiress). Or maybe Ralph did marry this Ada but she was not the mother of his children.
In the SGM thread linked above, John Ravilious (a highly competent researcher) Burke's Landed Gentry as saying, 'Sir Ralph de Brereton, Kt., of Brereton, Cheshire, born ca. 1210. M. Ada (widow of Sir William Handsacre, Kt.), d. of Henry de Hastings. Died before 1289'. Burke's is a very poor source this early and Ravilious thinks this is unlikely on chronological grounds, but after some of the discussion here I think it might be more likely than it first seems.
http://archiver.rootsweb.ancestry.com/th/read/GEN-MEDIEVAL/2002-02/...