Sometimes O'Connor will mention a specific treatise title, often he won't. It makes tracking down Luther quotes and putting them in context very tedious and difficult. Of course, if your typical Roman Catholic Internet warrior would read the actual sources available now, and quote Luther via those sources.... ah, never mind. That's wishful thinking.
Below are some of the main collections of Luther documents referred to by friends and foes of the Reformation. This is only a brief look. Citations in older books like O'Connor's and Patrick O'Hare's are often sparse, cryptic, fragmented, or in a foreign language. If you come across someone using an obscure Luther quote with a reference you don't understand:
1. If you're aware that it's a primary source from long ago, let them know you're in awe that they have had access to such a rare book. Tell them it's an honor to dialogue with someone who's read things like de Wette or Walch, and you look forward to being their pupil.
2. Ask them what the reference means. Chances are, they might not be able to tell you. That's a good sign they have swiped the quote from a secondary source, and haven't a clue as to the context.
3. If they can identify the reference as coming from an actual collection of Luther's works, ask them what specific treatise it's from and if they know any of the background as to the writing of the treatise.
4. If they do link you to an old Google Book in German or Latin, ask them if they can read either German or Latin.
5. Remember, if someone uses a quote, it's their responsibility to provide the context, not yours. If they can't provide an actual context and an historical context, their conclusions and interpretation are worthless.
Usually referred to as LW. English edition, published by Concordia Publishing House. You can usually find this set (54 volumes with the 55th book index) in a good library. Single volumes are relatively inexpensive and can bought new or used. There is also a CD ROM of this set. I've had this CD ROM for a number of years, and it's proved invaluable. Concordia is also releasing new volumes of Luther's Works.
Works of Martin Luther: With Introduction and Notes
Often referred to as PE. The Philadelphia Edition (Philadelphia: Muhlenberg Press). Sometimes called the Holman Luther, since it was originally published by A.J. Holman Co. This is an English set in 6 volumes. No need to go out and buy these, you can find them on line. They were published in the early 1900's.
WA: Weimar Edition of Luther's Works. 1883-.
Usually referred to as WA. D. Martin Luthers Werke. Kritische Gesamtausgabe; Weimar, 1883. This is the largest set of Luther's works, in German. It's arranged in four parts: Writings (WA),11 volumes of Letters (WA Br, or Briefe), 6 volumes of Tabletalk (WA TR or Tischreden) 9(or 12?) volumes of the German Bible (WA DB). This set was supposed to follow a chronological sequence, but more Luther material was found after the set had been put in motion. When newer items are found, or better source documents of previous material, they are be released in volumes entitled, Archiv zur Weimarer Ausgabe (AWA). The numbering of the Weimar set can be very confusing, like "WA 10, I, 2".
The Erlangen Edition
Usually referred to as EA. 1826-1857. Sometimes this set is referred to as "Dr. M. Luthers Samtliche Werke" or "E". The set includes German and Latin writings from Luther. The 68 German volumes were published 1826-1857, and revised later that century. The 38 Latin writings are specific to biblical interpretation (Exegetica Opera Latina, sometimes referred to as E op ex and Opera latina varii argumenti). They likewise were published in the 19th Century. This set includes 18 volumes of Luther's letters edited by E.L. Enders, and were also published separately. It also includes Luther's commentary on Galatians in 3 volumes.
Walch: The Walch Edition
1740-1753. 24 topical volumes. This was a set of Luther's works published 1740-1753 by Johann Georg Walch. This set is German, and Walch translated many of Luther's Latin writings into German. Sometimes this set is referred to as the St. Louis version, the St. Louis-Walch version, or the Halle edition, or Luthers Samtliche Werke, herausgegeben von J. G. Walch. It may be Abbreviated as "St.L" This set also includes writings by others, friends and foes of Luther. The set was revised from 1885-1910 (in St. Louis), and may not match up with the earlier set. Sometimes the revision is referred to as St.Lb. Volumes 15-17 contain rare Reformation history texts, and contemporary letters.
Dr. Martin Luthers Briefe, Sendschreiben und Bedenken (Dewette)
5 volumes of Luther's letters in German edited by Dr. Wilhelm Martin Leberecht de Wette. "The best collection of his Letters was edited by De Wette (5 vols., Berlin, 1825-8), with a supplementary volume by Seidemann (1856)" (source). "The Letters of Luther were separately edited by De Wette, Berlin, 1825, sqq., 5 vols.; vol. VI. by J. C. Seidemann, 1856 (716 pp., with an addition of Lutherbriefe, 1859); supplemented by C. A. H. Burkhardt, Leipz., 1866 (524 pp.); a revised ed. with comments by Dr. E. L. Enders (pastor at Oberrad near Frankfurt a. M.), 1884 sqq. (in the Erl. Frankf ed.). The first volume contains the letters from 1507 to March, 1519. For selection see C. Alfred Hase: Lutherbriefe in Auswahl und Uebersetzung, Leipzig, 1867 (420 pages). Th. Kolde: Analecta Lutherana, Briefe und Actenstücke zur Geschichte Luther’s. Gotha, 1883. Contains letters of Luther and to Luther, gathered with great industry from German and Swiss archives and libraries" (source).
Br:The Braunschweig Edition. 10 volumes of devotional writing, published 1889-1905.
The Clemen (ClL) or the Bonn Edition (BoA). 1825-1828. 8 German volumes. The first four contain complete treatises, 5-8 are selections from early lectures, letters, sermons, and tabletalk. The text is said to be superior to WA.
The Munich Edition (Mu). 6 German volumes, with 7 supplement volumes (Mu Erg), published in the 1900's.
Luther Deutsch (LD). 11 volumes, with 3 volumes of commentary.
The New Calwer Edition. 12 volumes in modern German.
Martin Luther Studienausgabe. 6 German volumes.
The Wittenberg Edition. 1539-59. contains 12 German and 8 Latin volumes. The material was topical, at the request of Luther. This volume contains some of the writings of Luther's opponents as well.
The Jena Edition. 1555-1558. 8 German and 4 Latin volumes, 2 supplementary volumes. John Aurifaber, one of the chief collectors of Luther's Tabletalk was one of the editors of this set.
The Allenburg Edition. 1661-1702. A poorly edited 11 volume German set.
The Leipzig edition. 1729-1740. 23 volumes in German, arranged topically.