Designation of product identity: The following items are designated Product Identity in accordance with Section 1(e) of the Open Game License, version 1.0a: Any and all Dungeon Crawl Classics logos and identifying marks and trade dress, DCC RPG, all proper names, capitalized terms, italicized terms, tables, critial hit and fumble descriptions, spell tables, the term “spell check,” the term “Mighty Deed of Arms,” the term “action die,” the term “spellburn,” the term “mercurial magic,” artwork, maps, symbols, depictions, and illustrations, except such elements that already appear in the System Reference Document.
That does leave most of it wide open. And there will be licensing of the PI for "official" 3rd party material. So I'm sure it's just a matter of asking for permission if you need to use the terms “Mighty Deed of Arms,” “action die,” “spellburn,” or “mercurial magic". The term "spell check" exists in the SRD so it can't really be claimed as PI. The OGL doesn't allow for duplicate terms with different definitions where one definition is OGC and another definition is PI. Once it is OGC it is always OGC.
And as I said above, that copy of the OGL is invalid and legally none of the material is yet proper OGC because it does not include the SRD in section 15:
15 COPYRIGHT NOTICEOpen Game License v 1.0
Copyright 2000, Wizards of the Coast, Inc.Dungeon Crawl Classics Role Playing Game
, ©2011 Goodman Games, http://www.goodman-games.com
The 3.5e SRD needs to be referenced in the copyright notice (or the 3.0 SRD where the copyright is just 2000 and name list stops with Bruce R Cordell's name).
System Reference Document Copyright 2000-2003, Wizards of the Coast, Inc.; Authors Jonathan Tweet, Monte Cook, Skip Williams, Rich Baker, Andy Collins, David Noonan, Rich Redman, Bruce R. Cordell, John D. Rateliff, Thomas Reid, James Wyatt, based on original material by E. Gary Gygax and Dave Arneson.