The definitive list appears to be the one that was signed by the men. Casement reported 38 had signed to the Germans, and that seems to indicate that M O'Callaghan and Golden excluded themselves (unless they later added themselves after the 38 had been declared). There are a number of other lists, which must have been drawn up as negotiations with the men progressed.
Official List 24 Jan 1916 has 40 names who signed the declaration
List dated 18 Jan 1915 with only 23 names
Official List with 37 names if one removes Casement, Monteith and McGoey. M O'Callaghan and Golden are not on this list. The men in italics below did not sign the top list, and the ones in brackets signed the top list, but are not on this one.
Mahony's list of volunteers for Egypt in Dec 1915 is 32 without McGoey.
By the autumn of 1915 the Germans had all but abandoned any plans they might have had for a military invasion of Ireland. Casement and Monteith were instructed to "consider striking a blow at England... by joining the army for the invasion of Egypt and helping to free another small nation". When Casement and Monteith put this idea to the 56 members of the Irish Brigade on 3 Dec 1915, only 38 were willing to go along with the idea (Caement's figures, but he does send 38 signatures to the German General Staff). The Germans reacted to this rebuff by deciding to again treat the Brigade as normal prisoners of war, which in turn caused 24 of the 38 to retract their offer to serve Germany in Egypt. Mahony's list points to 33 volunteering.
These men never actually fought in Egypt, but were asked if they would volunteer to fight with the Turks against the British in Egypt. There appear to have been 22 men on Mahoney's list who not prepared to sign up for this putative expedition to serve in Egypt as a machine gun group.
Keogh lost touch after the war with the non-volunteers. Mahony describes how he handed back his corporal's stripes as he was not prepared to volunteer for Egypt. Golden and M. O'Callaghan seem to have been the other of the original NCOs not prepared to volunteer. This certain seems to have polarised the volunteers in the Irtish Brigade
1915 Dec 1. The men were paraded and Casement explained that it is.hardly probable that the invasion of the British Isles will take place. Casement puts for the first time to the men the thought of volunteering for service with the Turks to fight the British in Egypt. He asks them to think over the idea of striking a blow against England by going to the Eastern Theatre of War and joining with the Turkish Army for the invasion of Egypt and helping to free another small nationality which England strangely enough omits to free. 30 apparently volunteered immediately and Casement thought the rest would soon sign up. On the other hand Monteith writes in his diary that nobody was very enthusiastic. Casement writes to Wedel asking for permission to go to Constantinople to see the situation for himself.
1915 Dec 1. Casement tells Meyer that "fully 40 men " have volunterered for Egypt
1915 Dec 3. Casement at Zossen. Together Monteith and Casement interview the men on the question of going to Egypt, 38 of 56 volunteer. They are disappointed at the response. List given by Mahony of those willing to serve in Egypt. Mahony's list gives 33 volunteers for Egypt - one could postulate that Mahony might have removed himself and any close friends form the list to make then seen less extreme,
1915 Dec 9 Memorandum written by Casement to Count von Wedel, from Zossen
"In the event of the Irish brigade volunteering for this service, the Imperial German Government undertakes to make arrangements with the Austro-Hungarian Government for its transport of through that Empire to Constantinople, and to provide with the Turkish Government for the recognition and acceptance of the Irish Brigade as a volunteer Corps attached to the Turkish Army in an effort to expel the British from Egypt. "
1916 Jan 6, Casement informs Monteith that the detachment of volunteers for Egypt are to start training immediately, arms are promised, and the men are delighted.
1916 Jan 7. German General Staff agree the sending of the Irish Brigade to Turkey. Nadolny writes "the deployment of the men would be a relief for us"
1916 Jan 16. Monteith writes in his diary. The men were still kept as prisoners, no leave granted. This so exasperated the boys so much that 24 out of 38 who had volunteered for service in the East, withdrew their names. Of this I informed the General Staff at Berlin, through Captain Nadolny, who went into a towering rage and said he would send them all to the Western front. I said you cannot and will not do so, and to his question why, I said because I will prevent it, my men will do as I say. He went on to say that arrangements had been made to train the men as a machine gun battery and that negotiations were proceeding with the Governments concerned to pass the men through their territory on their way to the East. This was in my opinion humbug and subsequent events proved my suspicions to be correct. I was asked to see the men again and ask for volunteers, which I did; 38 again volunteered, all of whom signed an agreement to come with me and under my command. Sir Roger Casement has now the document filed with remainder of Brigade papers. After some time I wrote a letter to the General Staff asking if it was the intention of the Government to allow these 38 men to proceed to the Eastern theatre of War, and if not to give them some work to do, so that they would become self supporting members of the community and cease to be a charge to the German Government.
1916 Jan 24. Monteith writes to Nadolny to say that 38 men have signed the papers volunteering for the Egypt expedition. He points out that those who have elected not to volunteer are perfectly within their rights under the original agreement on the foundation of the Irish brigade.
The declatarion that the volunteers signed said
"We the undersigned after full consideration volunteer our services to be drafted as a fighting unit to the South East Theatre of war. ie Egypt, Asia. As soldiers we understand tht we are obliged to abide by the military regulations or laws of the force to which we may be attached and are willing to do so.
We enter into this agreement on the understanding that we will be commanded by Lt R Monteith our present commander or in event of his death by an officer of Irish nationality appointed by Sir Roger Casement.
After that the whole thing just disappears or gets overtaken by events. The American Irish were never happy with the men being sent to Turkey, and with the Easter Rising in the offing the idea seems just to have been shelved and quietly forgotten.