According to wikipedia, sRGB is a standard created in 1996, so yeah, it just wasn't used earlier. However at the end of the millenium you could create software that opens an image file saved in sRGB, and unknowingly apply some algorithm, like dithering, without converting it to linear space first.
There was gamma correction and other perceptually uniform-ish color spaces before 1996 and before sRGB. I was taught about the CIE set of color spaces xyY/XYZ/LAB/LUV in school and used them to write renderers before I’d ever heard of sRGB. And yes exactly right, before they know better, a lot of people will grab something non-linear and starting doing linear math on it accidentally. It’s still one of the most common color mistakes to this day, I think, but it was definitely more common before sRGB. People sometimes forget basic alpha-blend compositing needs linearized colors, so it’s a common cause of fringe artifacts. Things have gotten much better though, and quickly. A lot of game studios 20 years ago didn’t have much in the way of color management, and it’s ubiquitous now.
