When my dad first got into CB in 1972, 10 was the trucker channel. There was even a country trucker song that mentioned "channel one-oh" I saw one time on "Hee Haw".
Channel 9 was ALWAYS been the emergency/motorist assistance channel since the CB band was established. The trucker channel was moved to 19 due to a request from emcomm groups such as REACT and ALERT to reduce adjacent channel interference.
Channel 11 was the FCC designated calling channel. Once contact was established, stations were required to switch to another channel to continue the contact.
In my area (southeast Virginia), the boating/fisherman channel was 13. My dad had a CB installed in his sloop and mounted the antenna atop the mast. Channel 13 was very busy during the warmer months.
Channel 16, along with 17, 18 and in some areas 15 were by gentleman's agreement designated sideband channels. Many CB'ers I knew that had sideband capability were on 16USB or 17USB. One minor conflict was in Virginia Beach, channel 15 was an AM channel while next door in Norfolk, it was a sideband channel. I say minor because most of the VB AM15 usage was in central , eastern and southern VB. Closer to the Norfolk line AM'ers steered clear of 15.
Those were the days when CB was for the most part civil.