I`d like to challenge largest CoT value:
After I conquered all CoTs in Europe except Veneto and Novgorod in 1729 as Maya, Veneto rose to a stellar high value of 4110. The reason: nobody wants to trade in a pagan-owned CoT so almost all of Europe and quite a few parts of the world traded via Venice.
After I annexed Veneto a few months later, Veneto dropped to just 10 and Novgorod became the biggest.
Note: you cannot take this number directly off a save game. If I loaded a save from after my annexation of Veneto, Novgorod had a trade of 4491, however, when I let the time run until the next month, Novgorod dropped to just 4028. The record value of 4110 for Veneto is taken after letting the game run to the next month.
In that same year, Anglia, Ile-de-France, Liguria, Thrace, Mecklenburg, Kurland and Astrakhan all had a CoT value of 5, which may be a world record lowest CoT value.