Harvard referencing: order of sources with same authors and same years in the bibliography
What you need to do: Find out the rules of the journal. For many journals, your paper will not
even be sent for review until the production staff has checked that the
references are in exactly the required format.

What you may want to support: Some journals in my field have started a policy to list all authors (up to three or four)
in the text of the paper: so it might be 'Smith, Zelda, Yates (2001)'.
The idea is that this gives name recognition to young, minority, and women
authors, who tend to be less often listed first. 
This policy evolved as influential
authors (some of whom serve on publication boards) began to insist on a change toward listing multiple names. 

It helps
that papers with long lists of authors are not especially common in my field.
Also, 'Smith, Hernandes, Chan (2013)' doesn't take much more space
than 'Smith et al. (2013)' and no journal budget seems to have suffered from
the change.