Those still with us will earn our money from the Further Education Funding Council.
Those who came briefly and thought better of it, or who left because they couldn't afford it, or who got the job they were always hoping for - all are now phantoms.
They earn us nothing, no matter what time and effort we put into recruiting and counselling them.
Fair enough, that's the system, and as we head towards the next census date we shall concentrate on holding on to what we have and trying to get some more. But it's November 1 which is the biggest day, being the first one after what is still the main enrolment time of the year, September. It's hard to recover ground lost in September, hence the current outbreaks of back-slapping and breast-beating.
This method of counting students by snapshot is widely accepted now, but is it the best or the only way?
Any photographer will say that a true photograph is one which prints everything in the viewfinder, not one which has been edited, or "cropped" as it's called, to give a partial or more favourable impression.
The great artists of the camera insisted on this, although there are rumours that the famous Henri Cartier Bresson was a closet cropper. The skill, or trick, is to exclude all extraneous or distracting information. You have to point the camera in the right direction to be sure of showing what you want to show. It helps, too, if the subject of the picture stands still. If only that were true of colleges where, in fact, nothing ever stays the same for long.
So the funding council snapshot is actually a freeze-frame of a fast-moving sequence of entrances and exits. They don't seem to do it so much these days, but cinemas used to display stills from the main feature outside, by the box office. They were supposed to give you an idea of what you would see if you paid your money.
As I recall, they did no such thing. They were the best bits, but not necessarily the typical bits. In fact, on the way out, you would look at them again and feel cheated, so little relationship was there between the selected highlights and the real thing.
The purpose of those stills, of course, was not to let you count the actors, more to act as a come-on. More of a prospectus than an audit return.
But what about those school photographs which had everybody lined up, standing on chairs and tables, in neat rows?
Naively, I had thought they were meant to be souvenirs to look back on years later for early evidence of subsequent crime or creativity on the scrubbed faces of my classmates.
Now I know better. These were key pieces of evidence for accountancy purposes: here were the staff, smiling for the camera, verifiable against the payroll. And here were the students gathered together so that the local education authority or the governors could check the numbers against the school's records.
Brilliantly simple; all you need is a copy of the photograph and a magnifying glass, then you multiply the faces by the unit of funding, or the fees, and you have the budget. Just to make doubly sure, you charge students for their personal copy of the audit evidence. We in the colleges still have a lot to learn.
Should we simply copy the scheme? We could line up all the staff and students in front of one of those cameras which move slowly round in an arc. It would need a football stadium, but it could be done. Each person could wear an identifying placard round their neck, with their name and course clearly printed on it.
The principal would sit in the middle, holding up a newspaper with the day's date displayed. Instant, irrefutable evidence. Of course, you would have to be careful that some fly characters didn't slip off their chairs once the camera had passed, run round the back, and reappear on the other end.
That would be double-counting, or multiple enrolments as they are now known, and we wouldn't want any of those. They might, in any case, be picked up by the scrutineers who would spend happy hours going over the blow-ups.
The big picture would have other advantages too. Suitably cut up and mounted in plastic holders, you would have foolproof student passes on the cheap. This would make life a lot harder for those spectral students who are rumoured to haunt the system, never enrolling, drifting in and out of libraries, canteens and, when all else fails, the occasional lesson, eventually becoming so familiar that they are assumed to be legitimate.
Some staff come into the same category. Catch one, however, and if they can't match their pass to the master, perhaps by now enlarged for easy reference into a mural, then out they go, or, better still, they are swiftly enrolled in time for the next snapshot.
Soon, all this will be swept away and consigned to sepia-toned history. The individualised student record will show precisely who has come, what they have done and where they have gone. Swipe cards will tell us even more: not only who is on the premises, but which room they are in and how long they have been there.
We will have more information about our students than we can sensibly handle. We do not require the information, although we may use it as it passes through the system. It's the funding council, in the interests of public accountability, which must ensure that we in the colleges know whom we've got. But whereas management information systems are fallible and college principals notoriously unreliable, the camera cannot lie.