This article centres on the impact the CISG Convention has had on the national and international development of law. It focuses on the rules in Art. 35 CISG, as the contents of the provision has gained wide recognition in a number of jurisdictions. However, this recognition has resulted in changes and alternative expressions of the legal contents of the provision. If the provision is used as a model for preparing national as well as international rules but is changed more or less extensively, the question is whether these rules have to be interpreted and applied in the same way as the Convention rules, or whether legislators intended the new rules to have different and separate contents and objectives. The following analysis will show that it is sometimes impossible to determine whether this was intended or not, and this leads to uncertainty as to the contents of the new rules. The thesis of this article is that these uncertainties can be avoided if the focus is shifted to the method used in preparing the new rules. This thesis should be seen against the background that doubts appear to arise because it is uncertain whether legislators intended consolidation with the rules in the CISG, or whether they intended proper codification based on the rules of the CISG - a difference that can explain the different interpretations of the contents of the new rules.