This was debunked long ago
>They claim that the 1940 World Almanac gives the world Jewish population as 15,319,359, while the 1949 World Almanac gives the world Jewish population as 15,713,638. In their view this makes it impossible that 6 million Jews died, even given an extremely high birth rate. They therefore claim that either the figures are wrong, or the Holocaust, meaning the deliberate extermination of millions of Jews, cannot have happened.
In fact, contrary to the claims of "revisionists," the 1949 World Almanac gives the world Jewish population as 11,266,600. Moreover, it revises its estimate of the World Jewish population in 1939 upwards, to 16,643,120. Thus, according to the 1949 World Almanac the difference between the pre and post war populations is approximately 5,376,520.
>In addition, rather than using more accurate census figures and other records, Holocaust deniers rely on a popular compendium whose methodology of assessment is unknown, and whose estimates have varied significantly. For example, the 1982 World Almanac gives the world Jewish population as 14,318,000, while the 1990 World Almanac gives the world Jewish population as 18,169,000, and the 1996 World Almanac gives the world Jewish population as 13,451,000. Either 3.7 million Jews appeared unnoticed between 1982 and 1990, and then 4.5 million Jews disappeared equally unnoticed between 1990 and 1996, or the World Almanac is not a particularly reliable source for accurate estimates of worldwide Jewish population.