Abstract: During programming of memory cells, calculating sigma bits for cells programmed at each program level based on attributes of the cells, such an index representing a cell's bit location in the memory array. For example, summing the indexes with an increasing weight factor, such as factor-of-2. During read, new sigma bits are calculated and compared with the stored sigma bits. A difference between the new sigma bits and the stored sigma bits may define a unique combination of indexes, enabling searching for, finding and correcting the read errors. The sigma bits may be used to correctly identify which cells were programmed at which program level, despite threshold voltage drift and/or overlap. Programming may be performed with advertent overlapping distributions, and the bits can be sorted out.