If the egg is squishy and moldy it has probably gone bad. I always keep them for a while anyhow just to make sure, but once it has caved in, molded over and smells bad you pretty much know it's time to toss it. If there is a hole or small crack that could cause some of the fluid in the egg to leak out a bit and that's what you see on the tip. Once the shell has been breached in any way, the contents will quickly dry up and whatever is inside will go bad.