Events occurring outside of good time intervals (GTIs) will usually be discarded before the TS is made. Where the collection region overlaps just one ccd/node, flux discarded in this way is lost 100% and cannot be reconstructed. In these cases the value of the exposure is set to zero.
Reconstruction is possible where the collection region overlaps more than 1 ccd/node, not all of which are outside GTIs at the same time, or within time bins which contain a GTI boundary.
GTIs are extracted from the data subspace (DSS) of the relevant TS.