Minefields are supposed to be mapped and documented; a modern army will do that until the situation becomes too urgent.
Cluster munitions are inherently much more difficult to map. I doubt that many armies even try. Of course, the density of unexplored cluster bombs will be lower, since the great majority detonate on impact (or proximity): 90% in most cases. But clusters are still regarded as areal denial weapons simply because that 10% UEX is so dangerous.
A minefield is easier to clear if it's mapped and recorded, of course.
But I wonder: how many cluster bombs are deliberately fused to work as mines?
ETA: Modern mines and cluster bombs can be built to disarm themselves after a period of time, lessening the risk from uncleared fields. How long a period of time? Well, ask the army that deployed them. Ask nicely.
But not quite completely. There's always a few that don't function as designed; no engineer will ever pretend there aren't.
If I now would like to be done with this topic, I know you'll understand.