Methods, systems and computer-readable storage media for determining a new optimal read threshold voltage associated with a group of pages of non-volatile memory. It is determined whether the current optimal read threshold voltage associated with the group of pages is out of tolerance based at least in part on a retention drift history associated with the group of pages. Upon determining that the current optimal read threshold voltage is out of tolerance, reference cells associated with the group of pages are written with a pattern having a known statistical distribution of ones and zeroes. The new optimal read threshold voltage associated with the group of pages is determined by reading the reference cells, and the retention drift history associated with the group of pages is updated with the new optimal read threshold voltage and an indication of a new reference cell generation.