Yes CCN would certainly have those symptons. It will also happen very fast. Have they been under some sort of stress, change of diet ..anything can cause it. I lost a ewe last autumn to it, and despite her still being upright when diagnosed and quickly treated, she died in the night.
You are not really at fault for that, it is really difficult to spot AND treat in time. I am not sure if keeping some Vit B ready for such situation will help, as it is quite rare and the Vit B will probably go off in the meantime...