Section 9.4.1 explains how to combine all the existing images in a final mosaic, while Section 9.4.2 shows how to merge different lightcurves and spectra.
Please be aware that it is not advised to combine results from all the mission, because of the evolution of the ISGRI detector. Only results from periods of time during which the instrument has not changed substantially should be used for direct combination of results. As a rule of thumb, these periods are of the order of six months, but a scientific validation should be performed by the interested scientist.