Yes, it can be considered and is a reliable source, not just because all claims of it being forged or changed have been resolved since 1989 the latest but also because its contents mesh with previous and later documents.

So, the Hoßbach Memorandum or Hoßbach Niederschrift are the notes of Oberst Friedrich Hoßbach detailing a Hitler monologue from November 5, 1937 held in front of high ranking officers of all branches of the Wehrmacht and various notables from the foreign office, which go into detail concerning Hitler's plans for Germany's violent expansion and take over of other European states. Crucially, the Hoßbach Memorandum contains a concrete time table as laid out by Hitler, which in 1937 spanned to 1942/43. This according to Hitler was the latest possible date by which Germany should start its violent expansion into other states and the intermediate goal was to make sure that France and Britain were not in position to join this coming war against the Soviet Union that in Hitler's mind was inevitable.

Five days after the meeting, Friedrich Hoßbach, the Wehrmacht Adjudant for Hitler, wrote down his notes for the meeting, which focused on what Hitler had said and layed out. The notes didn't include the reactions of the audience because – as Hoßbach later laid out – it was to preserve Hitler's thoughts for prosterity. Hoßbach then deposited his notes in the archive of the Wehrmacht High Command (OKW).

From there in 1943, a member of the historian's department of the German General Staff, Oberst Graf Kirchbach, commissioned a transcript of Hoßbach's note. Kirchbach was a member of the anti-Hitler cell in the Wehrmacht that later became famous for their attempt on Hitler's life in July 1944. Kirchbach recognized the worth of the protocol to show the long lasting preparations for war. For safety and safekeeping he then went to deposit the transcripts with his brother in law, Heinrich von Martin, in January 1944 in order to keep it safe, as can be gleaned form the documents that von Martin handed over later to the Institutie for ccontemporary history in Munich here.

Von Martin would go on to hand over the Hoßbach notes to the British military authorities in 1945. They too recognized what they had at their hands and especially since they had also discovered the original Hoßbach had written in 1937 among the rubble of the OKW archives. However, then a mistake happened: Some of the British investigators for the Nuremberg trial misplaced the original so what remained and was ultimately handed into the Nuremberg trials as document PS-386 was a typewritten copy of the transcript commissed by Kirchbach in 1943.

This is where the allegations that the document is unreliable come in, since especially those indicted in Nuremberg tried to attack the document as changed, not a verbatim transcript, only containing notes and not being a protocol in the first place. However, Hoßbach himself, questioned in Nuremberg in 1946 and later in his own book confirmed that the type-written copy contained the same content as his original notes.

Despite this, a variety of Holocaust deniers and Neo-Nazis seized the chance and continued to claim for years that the memorandum was fake or had been changed or what have you. This however, has virtually stopped since 1989 when in previously not accessible British files, the original surfaced as it had been misfiled apparently in 1945. Furthermore and around the same time, parts of Ludwig Beck's – another high ranking Wehrmacht officer who took part in the July 1944 plot – estate surfaced in East Germany. Beck's estate incldued his own notes from the November 1937 meeting and unsurprsingly their content confirmed Hoßbach's notes: Hitler planned for war that was supposed to start the latest in 1942/43 and to that end Germany needed to find a way to deal with GB and especially France since they wanted to focus on the east.

And there it is: We already had a copy of the notes that were confirmed as correct by the author, Hoßbach, himself but by 1989 not only had the original resurfaced again but also another piece of evidence appeared that confirmed the content once again.

Furthermore, a wealth of additional sources confirms that Hitler wanted and needed war: Already in February 1933, Hitler gave a talk to the Reichswehr leadership that was summed up in three different sources, the Liebmann-Aufzeichnung, the Mellenthin-Diktat, and a summary by the Communist Party's secret service. In that talk, Hitler leaid out to the Reichswehr leadership that his aim was to build up the Reichswehr further and that it was absolutely necessary that in the next decade Germany would need to aggressively expand into the east for living space.

This, in conjunction with the entire economic policy of the Reich, which according to Adam Tooze reached the point where the leadership had to decide whether they needed to violently expand into new territories or completely stop what they were doing in 1935, shows that from very early on in the Third Reich, Hitler and the rest of the leadership planned for war.

By 1937 these plans had become much more concrete and the Hoßbach memorandum shows that they now had a very concrete and comparatively precise time table for war. The entire meeting was to make sure that foreign office and Wehrmacht leadership were working towards the same goal, namely that the army was ready to move on Austria and Czechoslovakia while the foreign office made sure that social tensions in as well as foreign engagemenments of France were high enough and complicated enough that France would buckle and allow Germany to expand into Austria and Czechoslovakia. Something that came to pass not even 12 months later.

Sources:

• Adam Tooze: Wages of destruction.

• Bradley F. Smith: Die Überlieferung der Hoßbach-Niederschrift im Lichte neuer Quellen. In: Vierteljahrshefte für Zeitgeschichte 38, 1990.

• Johannes Hürter: Hitlers Heerführer.