Uhm, about 6-20 very common ones,, though total count is close to 200. And these have variants. But even within just betacoronavirus 1 OH49 (10% of colds or thereabouts) immunity is not persistent.

It is just mild enough. There's another one alphacoronavirus in about 5% of colds that is much worse. (Not counting SARS group.) Mind you parallel infection with multiple viruses is common.