A secondary issue is that judges in appeals courts are generalists, not tax or state aid experts. Despite this, they get landed with the hardest cases - situations that haven't been seen before which throw up new legal issues - and need to figure out what to do. Most of the time they get it right. Some of the time, they mis-interpret the law and get it wrong. That's why we have the appeals process.
So where are we up to in terms of this case, and how many more flip-flops we can expect? This article is citing an advisory opinion of one of the EU's Advocate Generals (themselves, very senior judges). These advisory opinions are issued prior to the CJEU (the highest court) making a final ruling. They are there to guide the CJEU so that the final ruling is as good as possible. Although this specific case should be finalised after the CJEU makes its ruling, I'm sure the case law will continue to evolve in the future as multinational companies push the boundaries of the EU's tax and state aid regimes.