Methods of operating nonvolatile memory devices may include identifying one or more multi-bit nonvolatile memory cells in a nonvolatile memory device that have undergone unintentional programming from an erased state to an at least partially programmed state. Errors generated during an operation to program a first plurality of multi-bit nonvolatile memory cells may be detected by performing a plurality of reading operations to generate error detection data and then decoding the error detection data to identify specific cells having errors. A programmed first plurality of multi-bit nonvolatile memory cells and a force-bit data vector, which was modified during the program operation, may be read to support error detection. This data, along with data read from a page buffer associated with the first plurality of multi-bit nonvolatile memory cells, may then be decoded to identify which of the first plurality of multi-bit nonvolatile memory cells are unintentionally programmed cells.