Note it doesn't say "20 million Jews", so do not compare it to previous numbers like 6 millions. It includes political opposition, disabled people, homosexuals, Poles, Soviets etc. Especially with Soviets it depends on how you count. Are civilians murdered by Nazis outside of camps still a part of holocaust?

That sounds ludicrous. I'd like to see their reasoning and citations.

I work as a guide in Berlin, as well as at the Sachsenhausen Memorial outside of Berlin.

I know exactly the issue here, because I have come up against it before.

The problem is that many sources, including the article that you have linked to, mis-represent the 2009 USHMM study "Encyclopedia of Camps and Ghettos, 1933 - 1945".

What the study has actually said is ..

The lead editors on the project, Geoffrey Megargee and Martin Dean, estimate that 15 million to 20 million people died or were imprisoned in the sites that they have identified as part of a multivolume encyclopedia.

"Or were imprisoned". So .. this has frequently "morphed" into people saying "Did you hear that new research proved 20 million people died in the concentration camps!!!???".

As for the 42,000 number, this is correct. But the study includes every type of facility including death/labor/transit camps .. but also including labor placements, workshops, ghettos, detention centers, brothels, Germanization camps, euthanization facilities, POW camps, abortion stations, etc etc. The total includes every one of them, even if it only was open for a short time. Say, for example, a "satellite camp" containing a few dozen prisoners which opened for a only few months in 1941 for some specific task.

So .. yes .. the numbers are correct (according to this study), but they have to be qualified.

FYI, the very same US Holocaust Memorial Museum held an AMA a couple of weeks ago, which was linked in this sub. Here was their comment on numbers http://www.reddit.com/r/HaShoah/comments/2tvbhi/it_is_international_holocaust_remembrance_day_and/co2pghm