The issue of dynamic and static interpretation of tax treaties as well as materials produced by the OECD, such as the Commentaries to the OECD Model or the OECD TPG, has been widely discussed over the years by all stakeholders and with various outcomes. Depending on the jurisdiction, the approach taken towards the latest modifications of the above-mentioned materials (provided that they can be used for interpretation purposes at all) might differ. This can be clearly illustrated on the basis of the modifications introduced in the 2017 OECD TPG like, e.g., the DEMPE concept. In addition to time aspects, also the character of changes introduced through this concept can be discussed, depending on whether it can be treated as a mere clarification of the rules which already existed in the Guidelines or as an entirely new concept previously unknown to the taxpayer. These issues have been already subject to individual court decisions. This includes a decision issued by the General Court of the European Union (EGC) in the high-profile Commission vs Luxembourg case (commonly known as the Amazon case) as well as a decision issued by the Belgian Court of Appeal in Ghent. This article will dea...