Thinking back - I used to actively under-report. Even if I had done more, I'd just put down an hour and I would try hard not to put my report in unless pestered. In the end I changed my mob no so the group conductor couldn't contact me.
But I know that the elders would make up time for people who didn't report. They'd pull a figure out of thin air. Any elders (current or ex) posting here care to admit they did that?