Make sure that on the ballast the number, type and wattage of the tubes correspond to what is connected.
Make sure that it is 40W tubes and not 32W.
Lighting calculations 'supposed' to take into consideration average mean lumens, not initial and not end-of-life either, wall, ceiling and floor reflectivity, dirt factor as the reflective surfaces loose their efficiency and the optic do not transmit light as new, etc. In essence if it was designed for 200FC - which is EXTREMELY high - you should expect as much as 50% higher initial lighting levels. The lighting levels are also designed for the working surface, so in an office it would be about ~3' and not at floor level.