NPG publication date
I just came across an interesting bug(?) when grabbing a paper from Nature Photonics (http://www.nature.com/nphoton/journal/v6/n1/full/nphoton.2011.267.html). The reference for this paper is Nat. Photonics 6, 50-55 (2012). Note the year of publication. However it was "Published online" 13 November 2011. Interestingly, Zotero grabs the "Published online" date, rather than the date of physical publication, and therefore gets the year wrong when exporting, e.g. as BibTeX.
Of course, this phenomenon would only happen when a paper is published in advance online at the end of the year, to appear in print in the following year. Normally the year would be the same, and day and month usually don't appear in the list of references anyway. However it is a somewhat subtle way of getting a reference wrong.
Preferably, Zotero ought to grab the year/date of "actual" publication when one is available. How to handle papers that are grabbed online before physical publication is an intricate question.
Of course, this phenomenon would only happen when a paper is published in advance online at the end of the year, to appear in print in the following year. Normally the year would be the same, and day and month usually don't appear in the list of references anyway. However it is a somewhat subtle way of getting a reference wrong.
Preferably, Zotero ought to grab the year/date of "actual" publication when one is available. How to handle papers that are grabbed online before physical publication is an intricate question.
In addition you can use Google Scholar to discover items but you should go to the publishers' websites to get your citation metadata. The same with Microsoft Academic Search.
Of the various sources of aggregated data, does any perform better than the rest on average?
The offending article has DOI 10.1177/1354066111413308
Retrieve Metadata will work somewhat better - and more often find the DOI and use CrossRef - in the next Zotero version, due out soon.