One thing I've run into while researching this is Allied bombing of railroads and trains late in the war.
Even when Jewish forced laborers survived numerous labor camps, their evacuation west in 1944-1945 didn't result in survival.
One example:
[A]pproximately 500 women on the camp grounds had to board a train that was waiting for them. After they boarded the train, it left the Salzgitter area. On April 8, 1945, the transport arrived at the goods railway station in Celle, where that evening it became a target of an Allied air raid. More than half of the women from the Salzgitter-Bad subcamp lost their lives during the bombardment.
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SALZGITTER-BAD
Less than a month before they would have been "Holocaust survivors," the Allies turned them into "Holocaust victims."
This camp included Jewish and non-Jewish laborers and the USHMM states barely any documentation of the camp exists, despite the inmates working in important armaments production.
The USHMM Encyclopedia could serve as a base for an interactive map of population flows, but their entries include no metadata that would help. It would all need to be extracted and organized. Some of the most important dates and events are completely unsourced.
The reliance on Stalin-era trial testimony and single-eyewitness accounts of large killing actions would have to be closely scrutinized. Of course, multi-eyewitness accounts introduce large discrepancies.
One final point: the Soviet sources usually refer only to "Soviet citizens," where USHMM/Yad Vashem often refer to "Jews." But 2 million "Soviet citizens" surviving after the war were repatriated back to the USSR by Britain and the USA in the various "Operation Keelhaul" actions. Others killed themselves to prevent repatriation. Soviet soldiers and the
Ostarbeiter forced laborers made up the largest number of repatriates.
> survive the labor camps
> survive the train car bombings
> survive the railroad delays causing starvation
> make it to a camp
> survive the typhus epidemics ravaging the camps
> make it to a DP camp run by the Americans or British
> get forcibly repatriated to the Soviet Union
> get shot by NKVD
> Holocaust survivor or Holocaust victim? Or both?