Some researchers assume that official and unannotated codes are the same thing. They are not the same, and they are used for different purposes. To eliminate any confusion, I will first explain the difference between official and unannotated codes, and then discuss when each should be used.
An official code is one that is published by the government or at its direction. Unofficial codes are sometimes called commercial codes, and they are published by commercial publishers without government direction.
Annotated codes are simply codes that have annotations—references to related judicial decisions, administrative materials, and secondary authorities—in addition to the text of the statutes. Unannotated codes have just the text of the statutes, usually with brief notes indicating when each section was added or amended.
All versions of the same jurisdiction's statutory code, whether official or unofficial, annotated or unannotated, use the same numbering scheme. You can use the same citation to look up a statute in any current code, even though the code abbreviation and date parenthetical are different. That is why you don't need parallel citations for statutes.
Although most official codes are unannotated and most unofficial codes are annotated, that is not always the case. Some of you have already used an unofficial unannotated code on Westlaw. For Illinois, the database IL-ST-ANN is the annotated code and IL-ST is the unannotated code. They are both unofficial.
The advantage of using an unannotated code is that it is much smaller. When you search an unannotated code online, you are only searching the statute, so you don't get false search results where your terms appear only in the annotations and not in the text of the statute.
The importance of official codes is that many publishers, including most law school journals and law reviews, require you to cite to the official code if the statute has been around long enough to have been incorporated into the official code. Since all the codes for a jurisdiction are numbered the same, you can do all your research in an unofficial code and use the official code for your final citation check—to be sure that your cited statutes are included in the unannotated code and to get the date for the parenthetical.