Why do some documents have more than one DOI? I was looking for the DOI of a paper (namely Evaluation of Antibacterial Activity of Asparagus racemosus Willd. Root) on http://search.crossref.org/, and found two DOIs associated to it:




http://dx.doi.org/10.1002/(sici)1099-1573(200003)14:2&lt;118::aid-ptr493>3.3.co;2-g 
http://dx.doi.org/10.1002/(sici)1099-1573(200003)14:2&lt;118::aid-ptr493>3.0.co;2-p


Both DOIs point to the same document (http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1099-1573(200003)14:2%3C118::AID-PTR493%3E3.0.CO;2-P/abstract).

How comes?
For the specific articles you gave as an example, the first DOI has an error in the article title in its metadata. The second has the correct title.


The DOI 10.1002/(sici)1099-1573(200003)14:2&lt;118::aid-ptr493&gt;3.0.co;2-p was issued first. In the metadata for that DOI, the title is given as Evaluation of antibacterial activity ofAsparagus racemosus Willd. root (missing a space between "of" and "Asparagus").
The DOI 10.1002/(sici)1099-1573(200003)14:2&lt;118::aid-ptr493&gt;3.3.co;2-g was issued a few days later, and in the metadata, the title is corrected to Evaluation of antibacterial activity of Asparagus racemosus Willd. root.