Thanks again . . .
I set 'statdisplay' to use the 'access.log' file because I can control (to a certain extent) what's in it. For example, the 'logstats' plugin has a facility to screen out all accesses from (named) bots. And also accesses from admin etc. With no 'bot' screening, the 'page view' stats are misleading to the point of being, errr . . . more or less hopelessly misleading.
So I use the 'access.log' route. However, I'm pretty well convinced that 'statdisplay' is using cached data. What makes me think that? Beacuse if I delete the 'access.log' file it makes no difference to the current data that 'statdisplay' displays !
So my quesion is again, where has that data gone, and can I get it back? I've lost four months or so of user traffic data.