I included some of this, but I'll now add the year-end rankings for each player Austin beat on clay:You might want to check these players for their actual seeding in the actual tournament she beat them in and check their WTA ranking. Some of these efforts feel like padding. If Evert beat these same people in these years, it would have been sited as evidence of how weak the draw was, not how strong the draw was. Heck, even when they won those slams, it was considered evidence of how weak the draw was!
1977 Hilton Head: Dianne Fromholtz #8
1977 U.S. Open: Sue Barker #5
1977 U.S. Open: Virginia Ruzici #16 (won the French Open the next year).
1978 Hilton Head: Rosie Casals ?? #16 in ELO according to Tennis Abstract
1979 Hilton Head: Evonne Goolagong #4
1979 Hilton Head: Kerry Reid #9
1979 Fed Cup: Kerry Reid #9
1979 Rome: Mima Jausovec #20
1979 Rome: Virginia Ruzici #13
1979 Rome: Chris Evert Evert #2
1979 Rome: Sylvia Hanika #16
1979 Wightman Cup: Sue Barker #10
1979 Wightman Cup: Virginia Wade #8
1980 Orlando: Andrea Jaeger #7
1980 Fed Cip: Hana Mandlíková #4
1980 Fed Cup: Olga Morozova n/a (USSR didn't let her play the pro tour due to apartheid, but she took part in Fed Cup)
1980 Fed Cup: Wendy Turnbull #8
So, 11/17 of these wins were over top 10 players, 15/17 were over top 16 players, one was over #20 Jausovec, who had just won and made the finals of the French the past two years, and one was over an involuntarily retired Morozova.