Versioning citations in PubMed.....

http://www.nlm.nih.gov/pubs/techbull/jf12/jf12_pm_versioning.html

Versioning in PubMed

Torre S. Versioning in PubMed. NLM Tech Bull. 2012 Jan-Feb;(384):e6.
2012 February 15 [posted]

PubMed now supports versioned citations. Revisions, scientific updates, and updates of reviews are examples of content that could be versioned. Versions are not intended for correcting specific errors in an article, for which published errata notices should continue to be used (see Fact Sheet).


How Will Versions Be Identified?

The PMID of a versioned citation will remain constant while each version will have a unique version number assigned by PubMed. The combination of PMID and version number in the format PMID.version will be a unique identifier. All citations not versioned will be considered version 1.

There may be occasions when a specific version will be deleted. In these cases, the version number assigned to the deleted version will be skipped, and the next version of the citation will be assigned the following number. Version numbers will not be reused.


Display of Versioned Citations in PubMed

Version information is noted on the Summary, Summary (text), Abstract, and Abstract (text), displays. On the Summary display, the version number is located before the journal title abbreviation. The article’s original publication date is retained, and the version publication date is enclosed in square brackets (see Figure 1).