One source of comparable data for Apple seems to have been ignored by the European Commission in their Decision against Ireland/Apple, unless they considered it best not to mention it. Apple's tax scheme is remarkably similar to the "Double Irish" arrangement, a tax minimisation device apparently used by a number of US multinationals, including (allegedly) Facebook, Google, IBM and Microsoft.
It seems reasonable to suppose, based on the information publicly available, that it was Irish tax policy to permit the Double Irish for any multinational group that sought to avail itself of it. This points to the possibility that the Apple rulings were not anomalous, but reflected standard practice. It is odd that this source of data for settling the question of whether there was selective treatment, and hence "state aid", is not mentioned in the EC Decision. It is difficult to imagine that Commission investigators were not aware of it.
Apple's corporate structure in Ireland appears to have differed in one respect from the standard Double Irish structure. Instead of using a two-company structure, Apple used a single company which was deemed split into (a) tax-resident branch and (b) non-resident head office. (It used this structure for each of two companies: Apple Sales International and Apple Operations Europe.)
The EC Decision spends some time arguing — not in relation to the Double Irish question but a different issue — that a branch has to be treated differently than a company. It is doubtful whether this is correct in a transfer pricing context, where one generally has to treat a branch as if it were a distinct legal entity. However, even if using one company rather than two affects the position regarding state aid, to omit any mention of the Double Irish in the Decision seems negligent.
Edited extract from 'legal opportunism and the collusion of powers'
