A buyer can model almost any risk. The one they cannot model is whether the seller owns the thing at all.
Once the income is normalised, a buyer turns to the harder question: can the seller actually convey what they are selling?
Most diligence findings are knowable risks. Flat income, weak history, a concentrated catalogue, a buyer can model these, discount for them, and still close. Chain of title is different in kind. If ownership cannot be proven, the buyer cannot safely exploit the songs at all, because any later use could draw a claim from whoever really owns them.
So the findings split into two families. Some haircut the price, they shrink the number but the deal survives. Others kill the deal, or freeze it until the defect is cured. The operator's skill is knowing instantly which family a red flag belongs to, because that decides whether you are negotiating a discount or walking to the door.
Take a £200k-a-year catalogue under offer. Everything below is the diligence that decides what (if anything) actually changes hands.