Walking back into a holding cell at the Edward A. Garmatz U.S. Courthouse in Baltimore in 1994, Corey Woodfolk recalled, he did not know exactly how much time the judge had sentenced him on a charge of conspiracy to distribute more than one kilogram of heroin.

At first, he thought that he had made out. That’s because U.S. District Judge J. Frederick Motz handed down his sentence in months instead of years. But Woodfolk said he noticed that his mother was crying in the back of the courtroom, and he started to do the math.