You are comparing apples and oranges. Estonians as a culture had been seafarers since 2000BC, that's ~3000 years of history when we get to CK start dates.
I am comparing 2 very pseudo historic ethnic groups in game within games timeframe. As I see it if you can answer affirmatively the question "Do these people had a habit of getting into boats and sailing to raid other people at some point around years 867- 1066?" then they get longboats and ability to sea raid. I think Curonians qualify. In any case Im not sure why you are so hanged up about boats, like, its one of the least fucked up things about setup of Baltic region.
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