Or it could be treated sort of like the start of WWII. For the US the first salvo of the war didn't come til 1941 when Pearl Harbor was attacked, and most people consider that as the "true" start of World War II (since before that, technically, only the countries on the Eurasia continent were at war, while no official act of war had been declared against the US). But for the rest of the first salvo of WWII occurred in 1938/9.
And the war in Asia was underway as early as 1931, when the Japanese invaded Manchuria. And Ethiopians would say it began in 1935 when Mussolini invaded them.
What you say is basically true, but unfortunately the Romulan War
novels don't make an effort to present the situation that way. There does seem to be a consensus among the book's characters that the war is underway by 2155.