Anymore, I flush every engine that comes through our doors and recommend that racers do the same if they plan on changing oils (ANY oils) since I'm so gun-shy of compatibility problems that DO exist.
When we dyno an engine for a customer, I am more careful than ever to ask what oil they are using to race with, and use THAT oil to break their engine in and make pulls on the dyno (with few exceptions.) If it's an oil that I do not regularly stock or can't get ahold of easily, then I have the customer provide their oil for dynoing. Pretty inconvenient, but the results are worth the effort by far.