The Chevrolet Warranty Book (Owner Protection Plan) covering all 1961 models, including Corvette, came in two versions. One had a blue cover (earlier) and the other had a green cover (later). Can anyone tell me when the changeover occurred (by approximate date or approximate serial number) and what period may have straddled the changeover? I know that the blue cover appeared at least as late as mid-November 1960, and that the green cover appeared as early as the end of March, 1961, but I haven't been able to refine the dates beyond this. Any assistance will be appreciated. Thank you.