Great question, and I'll first say "I don't know". But I have some ideas. The first is that (PLEASE DO NOT DO THIS!!!) when the Sun is low on the horizon and the light goes through a lot of atmosphere, one can (PLEASE DON'T!) look directly at it (IT WILL STILL HURT YOUR EYES) and when there are large sunspots, a person could see them this way. People these days photograph this kind of thing a lot; often, good pictures are posted on spaceweather.com as the 'pictures of the day' type thing. The second thought is that when an image is projected using a pinhole camera, one can see the spots fairly easily. While the idea of "cameras" may not have been around, all this method takes is a tiny hole and a flat surface - and can occur for example near a tree (small holes formed by leaves and the spaces between them) and a flat piece of wall or stone or cloth. So - it is possible to see the sunspots without any fancy equipment. I am a proponent of the pinhole camera - easy to make by poking a hole in a piece of cardboard.