Some Leather or Family Alcyoniidae corals periodically slough-off a thin top layer of tissue. This shedding process is apparently not a regenerative action, but one that serves to rid the coral's surface of accumulated waste, debris and algae. Once a coral has shed what could be described as a layer of "old skin", it's not unusual for it to appear larger and more magnificent than before.
Sarcophyton, Lobophytum and Sinularia species leather corals are those that regularly go through this shedding process, as shown in this sequence of Toadstool Mushroom Leather Coral pictures.
By using the Tridacna crocea Clam in this first picture as a gauge, you can get a general idea of the width and height of the coral before it shed.