Disagree. Cut & paste diagrams are often thrown together in minutes. All trains are originally diagrammed - it's just which one they dump that causes the problem.
Sort of; if the number of diagrams does not equal the rostered staff on duty then they won't be. But I'll take your point that "originally diagrammed". It might just be that nobody is available for "Sheffield 1000" diagram.
Diagrams are then left uncovered by rostering, although on the day resources teams might shift people so the "least worst" crew diagram gets cancelled.