It has been stated that Morgen later claimed he simply mistook the name of Monowitz for Birkenau. However,
the description he gave at Nuremberg of the location of the gas chambers corresponds in substance and not only in name to Monowitz, and not to Birkenau:
So he is both claiming an informed opinion resulting from investigation and he gets it wrong. It's my understanding from photos that Birkenau consisted of barracks with related facilities and was not an industrial site. Monowitz was or contained a Buna (synthetic rubber) factory site, with chimneys, etc.
This still doesn't get you a banana, because Morgen corrected his mistake in a subsequent interrogation, without being prompted. At most he was conflating elements of Monowitz (the industrial site) with Birkenau, except that Birkenau definitely had chimneys on-site, i.e. the crematoria.
What you have failed to quote is Morgen's deliberately deceptive introduction of East European collaborators as guards around the camp he describes. There were no such guards at either Monowitz or Birkenau in the period of 1943-44 when it is known that Morgen investigated Auschwitz; there were however foreign collaborator guards as part of the Majdanek guard force in mid-1943, when he visited the Lublin area. Emphasising foreign guards was intended to reduce the culpability of the SS, he was after all giving testimony as a defense witness for the SS as a whole, which was being charged as a criminal organisation.
Auschwitz did receive a company of Ukrainian Trawnikis in spring 1943, but part of this unit mutinied in July, and the company was transferred, to Buchenwald, before it is known that Morgen arrived at Auschwitz for his investigation.
The entire gambit is pointless in any case, since Morgen was just one of fifty or more SS officers and men testifying to gassings at Auschwitz in 1945-46; behind the scenes at IMT, Otto Moll was brought in to be confronted by Hoess, resulting in a rather amusing exchange as Hoess shot down Moll's excuses, which made very little difference to his fate, as Moll was already under sentence of death for his crimes at Dachau. Moll tried his damnedest to minimise his role at Birkenau but did not deny the crime.
Morgen's investigation at Auschwitz was corroborated at this time by others from his team, interrogated quite separately - eg Gerhard Wiebeck. And Morgen mentions things which are well-documented, such as the burning down of a wooden barracks used by the political department, in an attempt by SS men to destroy evidence of their corruption. Grabner's arrest and trial is so frequently attested by other witnesses from Auschwitz and Morgen's team as to be completely beyond all reasonable doubt.
Morgen testified that Dachau and Buchenwald were relatively orderly at the times he visited them, claims that simply did not mesh with the evidence given by everyone else - about conditions at the end of the war. So he was disbelieved at the time by IMT and NMT judges alike, yet we know that his impressions were much more accurate for 1943, when he conducted his investigations.(1943 saw a halving of the death rate at Dachau, albeit in part because they assiduously transferred weakened prisoners elsewhere to lower the death rate. Buchenwald saw 3500 deaths among the now almost entirely non-Jewish inmates in 1943.) It must be tempting for deniers to cherrypick such remarks and pretend they applied to the entire KZ system throughout the war, ignoring the well-documented changes in the system as well as differences between camps.
Someone's lack of knowledge is not proof of a conspiracy or fraud, I have to add.
