According to this sites popularity charts, in 1990
Adelaide and
Isabella were equally popular for all ages; that is of all people living in the U.S. in 1990,
Isabella and
Adelaide occured with approx. the same frequency. In fact
Adelaide was slightly more popular than
Isabella from 1900-1950.
Isabella just came into popularity again (in 1990) a few years ahead of
Adelaide.
The more I look at that, the more possible it seems that
Adelaide could become seriously popular here. :(