The southern sky surveyed by DENIS is divided into three zones, according to the declination: "northern" zone (+2 > d > -28), intermediate zone (-28 > d > -58) and "southern" zone (-58 > d > -88). To know the slot number corresponding to a given right ascension, use the FOURBI tool (DENIS users restricted access). This will give you the date of observation(s) of this slot, and you can then go through the list of observed slots to have an estimate of the quality of this observation.