I open clocks at club/fed/combines and have come across instances where the winning pigeons rubber had being caked in mud so yes in some instances it must have happened at liberation. I remember years ago an old fancier in my club commenting on he's pigeons going down for a drink, he would say yeah! this pigeon went down at Lincoln (for example) he reckoned he could tell what part of the country it went down by the colour of the mud/clay on the pigeons feet. Bull$hit or not?