Andy Adcock
Worst person on Birdforum
So it would seem that any name changes will have to wait quite some time before (if) they appear in book form.7th edition is the most recent edition...most of the editions are largely the same, other than updates to taxonomy, distribution, vagrants, etc, as well as updates to illustrations. I think the biggest change is the coverage of subspecies in the most recent edition. 7th is the edition to buy.
Complete I believe has everything, although I have never owned the "regional versions". I don't think they are necessary versus the regional editions of Sibley, which tend to be far easier to carry around.
Would Sibley do a new edition just for new names?