You mentioned this on a number of occasions but you seem to have overlooked a significant issue, namely that the supposed 'leak' occurred in 1904, at least a year before Schlieffen finished the famous version of his plan. Samuel R Williamson writes in The Politics Of Grand Strategy that :Then there's one more possible use. Deliberately leaking the 1905 document to the French GQG would induce all three of the Entente members to start thinking offensively. All of the French war plans between 1875 and 1912 were defensive.
The story behind French acquisition of these German documents in the winter of 1903-1904 remains confused and uncertain. In 1932 Maurice Paléologue, who had been one of Delcassé’s assistants in 1904, asserted that a disillusioned German staff officer had betrayed the outlines of the Schlieffen Plan to French agents. Subsequent studies have cast grave doubts about Paléologue’s accuracy both on the alleged betrayal and in his summary of the new information. Certainly there was no question, as the French diplomat implied, of the Schlieffen Plan having been revealed, since the Plan did not go into effect until late 1905.
At this point in time, Schlieffen's planning did not involve the broad sweep through Belgium and the Netherlands but rather a more limited violation of Belgian neutrality which, according to Williamson, French Intelligence duly reported to the General Staff with some accuracy in August 1904:
Finally in August the General Staff drafted a memo embodying the new information and cautiously noting their uncertainties about it. This staff paper, comparable in many ways to the British war game, credited Germany with twenty-eight army corps. Of these, sixteen were expected to be deployed in Alsace-Lorraine, nine to be concentrated in the area around Aix-la-Chapelle, and three to serve as a link between the Lorraine and Aix-la-Chapelle deployments. The Staff thought the northern German corps would launch a flanking move through southern Belgium, south of the Meuse and Sambre, aimed at Chimay-MéziêresStenay; the German forces in Lorraine would, meanwhile, take the brunt of the French offensive. In this assessment French intelligence had in fact discerned the major features of the German plans then in force: Schlieffen did plan a limited enveloping move through southern Belgium while also advancing from Lorraine.