December 02, 2008 [Editor's note added]
PubMed® Entrez Date Modification for Older Citations
P ubMed citations are displayed in reverse Entrez Date (EDAT) order, i.e., last in, first out. EDAT is the date the record is added to the PubMed database and appears on the MEDLINE display format. Until now, the exception was to set the Entrez Date the same as the Publication Date (DP) on records with publication dates before September 1997.
Publishers may submit citation and abstract data for articles published prior to for the indexing start date in MEDLINE (see [link removed] PubMed Overview.) In order to prevent older citations from displaying with newer citations, or being included in My NCBI updates we are changing our policy for how the Entrez Date is set for older citations. Effective in late October, the Entrez Date will equal the publication date for citations that are older than one year when they enter PubMed. [Editor's Note: The effective date for this policy change has been delayed until mid-December 2008.] For example, in the future a citation entering PubMed with a publication date of April 15, 2002, will be assigned the EDAT 2002/04/15. This change is prospective only; the EDAT on existing records will not change.
Canese K. PubMed® Entrez Date Modification for Older Citations. NLM Tech Bull. 2008 Sep-Oct; (364):e12.