We do not know how many people developed AIDS

We do not know how many people developed AIDS in the 1970s, or indeed in the years before.

"The dominant feature of this first period was silence, for the human immunodeficiency virus (HIV) was unknown and transmission was not accompanied by signs or symptoms salient enough to be noticed. While rare, sporadic case reports of AIDS and sero-archaeological studies have documented human infections with HIV prior to 1970, available data suggest that the current pandemic started in the mid- to late 1970s. By 1980, HIV had spread to at least five continents (North America, South America, Europe, Africa and Australia). During this period of silence, spread was unchecked by awareness or any preventive action and approximately 100,000-300,000 persons may have been infected."Jonathan Mann ¹

We also do not know for certain where the AIDS virus HIV originated, but it is now generally accepted that the origin of AIDS can be traced back to Africa.