There is an overlap between the functions of a storage organ and a perennating organ, but they are in principle different. See Raunkiær plant life-form for a classification of perennating organs.  Resting buds are a perennating organ, but not a storage organ. The stem (body) of a cactus is generally regarded as having been modified to act as a water storage organ, but it's not a perennating organ, in that it's not what the cactus dies back to in an adverse period. There could usefully be some cross-referencing, which I will attempt.