So, please correct me if I'm wrong, but it's Sole Survivor when discussing the main character from Fallout 4, and Lone Wanderer when discussing all the others (Fallout, Fallout 2, Fallout NV)?

Fallout -> Vault Dweller

Fallout 2 -> The Chosen One

Fallout 3 -> Lone Wanderer (also the name of a Perk in Fallout 4 though)

Fallout NV -> The Courier

Fallout 4 -> The Sole Survivor

Fallout 4's protagonist is never referred to as the Sole Survivor at any point in the game. The only time we heard that term was when Todd Howard introduced Fallout 4 at E3, saying we enter the wasteland as the "Sole Survivor of Vault 111". Travis does refer to the protagonist as the Vault Dweller, though.

AHHHHH....it's all so much clearer now for this late-comer to the franchise. Thanks so much!