Where does Baldur's Gate & Tales of the Sword Coast separate?

I want to change my PCs alignment & I want to do it @ a defined point in the game.

So, where does BG end & Tales of the Sword Coast begin? My general assumption is that as long as my PC is on that direct story-line from Candlekeep to Nashkel to Beregost to Bandit Camp to Cloakwood to...killing Sarevok, then I am in BG. Everything else, Durlag's Tower, Xxart Village, Mutamin's Garden, etc. are 'Tales of the Sword Coast'? Am I correct? Do I have it backwards?

Same thing for BGII. What separates SoA from ToB?

Thanks. CT