Unless you find the signs of where the target changed his shoes, all you can do is to refer to your careful measurements of his stride and your appreciation of how he walks. If he tries to alter his gait, you may be able to detect this as an unnaturalness in the overall appearance of the trail, although this can be very difficult to determine. If the target discovers that he is being trailed, he may. Ageing Determining the age of a set of tracks is a skill which is often neglected, even by good trackers. With practice and dedication you should be able to determine the age of a fresh track to within 15 minutes.
Tracks can last for years under the right circumstances.
There are parts of the world where dinosaur tracks can be seen, perfectly preserved by fossilisation. But in general terms, a track begins to deteriorate as soon as it has been formed. Tracks with well-defined features always appear to be fresher than smooth tracks. Make an impression with your thumb in the ground along side the track so that you can see how the soil behaves. Each soil type behaves in its own individual way, so you will need to experiment with the local soil before following up a trail.