Culbert's estimate was not made for Esperanto alone, but formed part of his listing of estimates for all languages of more than one million speakers, published annually in the World Almanac and Book of Facts.
Culbets estimat var ikke kun lavet for esperanto, men udgjorde en del af hans oplistning af estimater for alle sprog med over 1 million talende som blev publiceret årligt i The World Almanac and Book of Facts, en udbredt amerikansk almanak.