The 1999 issues convey a whole new style of vogue from the previous stlye 10 years.
My intial thoughts were that there may have been a change in chief editor because there is such a dramatic change in cover style and when i researched into the recent editors i found;
Ailsa Garland (1961–1964)
Beatrix Miller (1965–1983)
Anna Wintour (1984–1987)
Elizabeth Tilberis (1988–1991)
Alexandra Shulman (1992 – present)
therfore from this information i can tell that there has been a change in editor over this 20 year so i can make the assumption that the main change in cover stlye is based on the change in editors style and the demand of the new generations.