I, too, usually have at least one DIS. My last hatch there were four. I consider them DIS if they never internally PIP. Not much you can do for them in this situation. If I am watching the eggs like a hawk I can usually save any that internally PIP but for whatever reason do not externally PIP because of malrotation etc. I place safety holes and keep a very close eye.With each hatch I've done there is usually one DIS...for whatever reason in lockdown the lil baby just dies. Never internally pips.