Did a bit more research and it does seem that tuna isn't an original ingredient as you say. Nigel Slater is good on this matter:I take the basic ingredients of things like compound salads or classic dishes from le repertoire de la cuisine,I take this as a little bible ,any other ingredients are add ons,
http://www.theguardian.com/lifeandstyle/2001/sep/02/foodanddrink.recipes