[saalweachter]

Yes and no.

In these programs it is standard to mark the animal in some way. In NYC, for instance, you clip the top of one ear of a cat after it's been processed.

So you catch ten animals, immediately let go any ones that have been marked, process the last one or two -- still more effort to catch, but less effort to treat.

[samus]

They could just not bother to catch them if they see ones with clipped ears. Also, catching them might be quite simple if you attract them with treats and treat them decently.