I have found relatives who are listed two or three times, and other people I know from the Jewish Genealogy Society I belong to have found their own relatives there more than once. Almost always there are minor variations in spelling of the first and/or last names. Sometimes the given name is listed in one entry in Hebrew and another in the deceased's native language--Polish, Russian, etc. It doesn't change the tragically high number of Jews who were murdered, but it does call into question the validity of the number counted in Yad Vashem records.
Justice Ministry: Information examined by AG about Gal Hirsch didn't come from police (Haaretz)
from the article: Holocaust facts: Where does the figure of 6 million victims come from?