16.1% switched from another team to Albion seems about right to me, despite what your average bitter Palace fan would say. That 16% made up of inward migrants to Brighton from elsewhere in the country, and those who as kids only followed "big" clubs on the telly. A lot of the 83% (like me)...
I don't think it counts who you follow as a primary school kid. I thought I supported Everton as the most popular kid in my class was from Liverpool and followed them so I did too (this is the Alan Ball era when they were good). I didn't even know where Everton was! It only really counts when...