On May 20, David Johnson walked across the stage at commencement and accepted his degree. Like the hundreds of other graduates there, his proud family cheered and celebrated his accomplishment. That achievement, though, was completed more than 20 years ago. Johnson, 75, finished his master’s degree in imaging science in 1989. But he missed the commencement ceremony so he could watch his son graduate from the State University of New York at Geneseo.