The total number of available visas in a particular employment category depends on the total number of visas available for that year, plus any unused family visas. In the employment category of visas, the minimum number per year is 140,000. In addition to the minimum 140,000 visas, employment visas also receive any additional unused visas from the family-sponsored visa category.
However of the 140,000 (plus the unused family visas), only 28.6% of these visas can be used in the EB-3 category, equating to around 40,000 EB-3 visas available each year. The EB-2 visa shares the same limitations and percentiles as the EB-3 visa. Furthermore, the United States has implemented a 7% annual cap on immigrants from any particular country, in both the family visa category and employment visas. So, if the number of employment visas was 140,000 for the year, and if the family based visas were 226,000 (their limit); then 7% of 366,000 (140,000 + 226,000) would only be 25,620 individuals, from any one nationality, eligible to receive visas between the two broad categories.
The United States Customs and Immigration Services department receives well over the 25,620 allowed applicants from India and China each year. In December 2017, nationals from China and India who applied in December 2005 just became eligible for their priority dates.