The organizations that issue styles change them from time to time and it sometimes takes months for the changes to make it into Zotero (like the APA's electronic sources guidelines change this summer). The same is true for all the commercial solutions too. This is yet another area where Zotero can really shine compared with RefWorks.
<citation> <sort> <key variable="issued"/> </sort> ...</citation>
CSL does not now support styling of et-al, but will soon.