Thanks for the second paragraph! I think I knew in theory that bustimes could do what you describe, but I didn't know how to do it.
It's not unknown for buses to run but not to track (shouldn't happen, but sometimes does), and from the other end I have seen a bus fly past showing "not in service" while it was tracking, so it's not absolutely definitive as to what did and didn't run - but it's as good as we can do.
Assuming the data to be correct, I now know that of 52 scheduled journeys on "my" route today, 40 ran out and 38 ran back. Would it be unduly harsh of me to consider that amount of non-runnage to be very poor indeed?
It is not perfect, but is is much better than the not-so-old days of going to the stop and just standing there not knowing anything - as there are no real-time stop displays where I live.
Yes, sometimes buses run but don't track, or lose tracking mid-route, or there is a delay to the data, or the drivers resets the machine mid-route (or does a changeover) so it looks as though it stopped short but then there is another entry where it starts tracking again.
When running 'not in service' my main local bus does still track but I can tell it is 'NIS' because it will be off-route whizzing round the bypass or along the A50.
My other local route, which runs a couple of times per day and is run by a small operator, sometimes doesn't track at all. Today it only tracked leaving the depot and for the first 30 minutes or so in service, then it stopped. I've no doubt it ran in full I just don't know whether the driver had his meal break at the leisure centre or the industrial estate today!
40/38 out of 52 does seem very poor.
One thing to watch out for is how recent the data is. When looking at the map, you can click on a bus and it will say how many seconds/minutes ago the data was updated. If it says five minutes rather than one I will miss it because it is four minutes closer to my house than I thought!
If you click on region/operator/map you can see all of that operator's buses on every route.
If you click on region/operator/vehicles you can see all of that operator's vehicles and when they were last tracked.
If the timetable page says 'tracking four buses (or whatever) then you can click on that and track all of the buses on a particular route - so you would see if they were bunched up - depends how frequent a route is.
Technically, as the website says, it is ticket machines you are following rather than vehicles.