We did our annual weight and balance refresher course recently. The opening task was to do a manual loadsheet.
After 2 to 3 minutes, all the FOs had put their pens down and were all smiling at each other looking on at the captains who were all scratching their heads, looking at what the guy next to them had done and saying "errr... ehm"
By the captains' performance at the annual refresher it was clear that all of them had "delegated" this duty throughout the year, so I'm guessing there is no legal requirement to be current.