You are correct that having been frozen it will shrink alittle, however mud will make the original print bigger and deeper than it would be on dry ground.

This photo shows the tracks of two different species. Coyote and bobcat. The coyote track at the top shows some sliding from forward motion. The coyote slipped in the mud! Below the coyote track are two tracks from a bobcat. They are the left front foot (clearly visible) and another track, which may be older, or it may be the left hind track of the same bobcat. This photo provides an opportunity to study the footprints of two species or wild predator. The differences in their tracks are apparent here.