The unfortunate situation with the NASA-JPL magnitude data is that it is usually a step or two behind the comet's current situation. C/ISON is apparently experiencing yet another slowdown in its brightening trend. The very latest reliable magnitude estimates put it at virtually no brighter than it was back in mid October. This would correspond to altering the NASA-JPL formula's absolute magnitude for C/ISON downward from M1 = 8.0 to closer to M1 = 9.0 at the moment. Unless the brightening trend quickly returns, the NASA-JPL magnitude predictions will fall further behind each day now.
Surprisingly, accurate/reliable visual magnitude estimates for C/ISON made by experienced comet observers have been amazingly few in number. This is a rather unanticipated situation for a major comet although morning comets admittedly are always less observed than evening ones. Things may improve during the dark of the moon over the next two weeks, but the comet's declining altitude by the start of morning twilight may well pose a further problem unless the observer happens to be favored with a very good view of the eastern horizon.