Those colds that you’re seeing represent common symptoms of many viruses (metapneumovirus, paraflu, influenza, rhinovirus, RSV, etc, etc ... and many of these have multiple subtypes which can be concurrently circulating). In other words, you’re noticing common symptoms not necessarily the same virus.

I've read that you can carry it for 1-2 weeks without showing symptoms. That might significantly change how the virus spreads compared to flu.

Peak cold symptoms last about 3 days. I never said 50% of the population have the same cold at once. 50% catching it over a 6 month period is very reasonable.