You are partially correct. The Spinghawk was one of his flagships, but he used another one before the Chimaera. Hint: it served as his flagship during the Exploration of the Unknown Regions.
Bonus answer: Springhawk during his time as commander of the Chiss Expansionary Force
Overall: Great read! I loved Thrawn's character from Heir to the Empire to the end
And thanks for reading. Thrawn is my second favorite character because of his genius. The Thrawn Campaign was a work of a true genius.