What I should have made clear earlier is that the task involves the logbook - the missing entries have NO logbook entry at all - the only indication I have that they have found the cache is the online log!!! There is no proof that they've even been near the cache, let alone found it, or completed the task.
To be honest, if they had just filled out the log I wouldn't have batted an eyelid this late on - but there are no entries at all in 3 cases.
Sorry, but for me, if they do not sign the logbook that would be enough for me to delete the log, never mind the task!!!!