Finding their 'possible'

"Was it simply through curiosity or was there another rumour about how to delay the donations?"

Simple curiosity. In chapter 12 of the novel Kathy explained it like this:

Then there were those questions about why we wanted to track down our models at all. One big idea behind finding your model was that when you did, you'd glimpse your future. Now I don't mean anyone really thought that if your model turned out to be, say, a guy working at a railway station, that's what you'd end up doing too. We all realised it wasn't that simple. Nevertheless, we all of us, to varying degrees, believed that when you saw the person you were copied from, you'd get some insight into who you were deep down, and maybe too, you'd see something of what your life held in store.

There were some who thought it stupid to be concerned about possibles at all. Our models were an irrelevance, a technical necessity for bringing us into the world, nothing more than that. It was up to each of us to make of our lives what we could. This was the camp Ruth always claimed to side with, and I probably did too. All the same, whenever we heard reports of a possible - whoever it was - we couldn't help getting curious.

The way I remember it, sightings of possibles tended to come in batches. Weeks could go by with no one mentioning the subject, then one reported sighting would trigger off a whole spate of others. Most of them were obviously not worth pursuing: someone seen in a car going by, stuff like that. But every now and then, a sighting seemed to have some substance to it - like the one Ruth told me about that night.