Antony Beevor, in the context of late April 1945 / early May 1945 in Berlin:
The French NCO claimed that they were forced labourers who had been press-ganged into uniform by the Germans when the Red Army launched its attack on the Oder. They were lucky to be believed. At that stage, Soviet troops did not know about SS tattoos. ...
When one of them came to a Swedish Waffen SS volunteer with the Nordland, he prodded him hard in the pit of the stomach and asked the same question. The Swede claimed that he was just an ordinary Wehrmacht soldier. 'Da, da. Du SS!' the Red Army soldier insisted. The Swede, who had destroyed his papers, including his passport, which showed that he had fought for the Finns against the Soviet Union, somehow managed a smile as if to say how ridiculous. The soldier gave up, not noticing that he was in a cold sweat. It took another six months before the NKVD discovered that members of the SS had 'their blood group tattooed on the inside of their left arm'.
I read the above passage and was surprised that the Soviets (and Allies) learned about the SS tattoos only six months after the end of the Battle of Berlin (so, around late October or November 1945).
Is this true and if so, why did they figure this out so late?
(This 1985 account about how Mengele got away suggests that the Americans already knew about the tattoos in May 1945. Did the Americans know about this but not share this information with the Soviets?)
Quotes above from The Fall of Berlin 1945, 2002, pp. 322, 392f (Google Books preview, might be hidden). (I added the bold font.)
In Beevor's Source Notes (p. 461), he gives this source:
p. 393 'their blood group tattooed ...', Beria to Stalin, 20 November, GARF 9401/2/100, p. 492.
I do not know how to access this source, but if anyone is able to, what does this source say?