Keeping a skills matrix current after the first six months

Almost every skills matrix is accurate on the day it is finished and decaying a month later. People move roles, certificates expire, new equipment arrives, and the spreadsheet stays where it was. The fixes we see are ownership and a trigger. Someone is named as owner of each matrix, and updates hang off events that already happen — an induction, a role change, a permit application, a shutdown plan — rather than a quarterly review nobody diarises. What keeps yours current, and what does it cost you when it is not?