The 2012 Amendment to the International Code of Zoological Nomenclature allowed electronic publication for nomenclatural purposes, but it neither explicitly dealt with electronic versions published or posted online before being integrated into a journal issue, nor did it define what a preliminary version is. This has resulted in controversy as to whether electronic ‘pre-publications’ are available for the purposes of zoological nomenclature. Here I propose a definition of ‘preliminary version’ in line with publishers' NISO guidelines. The nomenclaturally relevant version is the Version of Record which is the final, immutable, published version. All versions of an article previous to the Version of Record are preliminary and not published for the purposes of zoological nomenclature. The immutability of the Version of Record refers only to content. Bibliographical metadata (volume, issue and page numbers) are not considered content; when those get added or changed with the inclusion of a document into a journal issue, the content of the document does not change, hence the version remains the same: the Version of Record. Following those guidelines, the Version of Record is available for nomenclatural purposes even if the page numbers later change. The online ‘pre-publication’ models of the major publishers are analysed as to which are available for zoological nomenclature. Electronic supplements should not contain nomenclaturally relevant information as they generally are neither immutable, nor permanent, nor published in the sense of the Code.