The most recent is the way the Lisbon Treaty has amended the numbering of all the continuing articles from the Treaty of Rome (creating the European Economic Community (EEC)) or the Maastricht Treaty (creating the European Community (EC)) from its effective date, 1 December 2009. Almost all references to the EEC or EC are replaced by references to the European Union (EU), which now has its own legal identity.
In the UK a statute, unless it is consolidated, survives for as long as it contains provisions that are not repealed. Provisions that are not amended can therefore continue with their original numbering. New clauses inserted into statutes are given supplementary numbers (e.g. section 55A to 55E of the Data Protection Act 1998 discussed in out last post). This can mean that a statute can survive with only one clause in force (e.g. Statute of Frauds 1677)
In Europe, however, each major treaty consolidates and amends former treaties. Provisions that have not been amended since their introduction in the Treaty of Rome signed in 1957 have therefore regularly been renumbered, to the annoyance of practitioners. However, for competition and regulatory lawyers and fans of George Orwell, there is at least the consolation that the article dealing with anti-competitive agreements that was formerly Article 85 EEC then Article 81 EC is now Article 101 TFEU (Treaty for the Functioning of the European Union). The abuse of dominance article becomes Article 102 TFEU.
Disputes will also now be heard first by the General Court (formerly Court of First Instance) or by the Court of Justice (formerly the European Court of Justice or ECJ). References to the Court of Justice will be made under Article 267 TFEU (formerly Article 177 EEC or Article 234 EC).
Expect a certain amount of confusion until everyone gets used to the new numbering.