According to BSEN 10253-2, the thickness preferred for DN800 pipe is selected by 8mm, 10mm, 12.5mm & 25mm. Since the pipe thickness is 11mm and the fitting thickness cannot be thin than pipe, therefore 12.5mm thickness would be selected. The thickness tolerance is +20% -0.5mm. Therefore the thickness range should be 12 to 15mm, your measured thickness are all within the standard requirement.