So I came to camp a Spectral Shroud this AM and have spent the better part of 4 hrs without seeing a single Spectral Librarian and only one Failed Crypt Raider. I haven't been able to find much to back it up, but tessmage does hint that these guys should be 50/50 chance named/placeholder unless it was less then changed at some point. Are these percentages off (I'm guessing they're either 10% or 25% chance to spawn now).
Link to Spawns on Tessmage