3.3.2. Additions and numbering
Where articles, numbered paragraphs or other subdivisions that are identified by a number or a letter are inserted into the enacting terms of an existing act, they are given the number or letter of the preceding subdivision of the same level in addition to the letter ‘a’, ‘b’, ‘c’, ‘d’, etc. For example, articles inserted after Article 1 become ‘Article 1a’, ‘Article 1b’, etc. Likewise, an article inserted between Article 1a and Article 1b becomes ‘Article 1aa’.
Special rules are to be applied in the following cases:
Where articles, numbered paragraphs or other subdivisions that are identified by a number or a letter are inserted, the articles, paragraphs or other subdivisions that follow should not be renumbered because other acts may already refer to them. Renumbering should be carried out only in the case of codification or a recast.
(Source: Joint handbook, Section C.9.3.2.)