Your Mt Evelyn relatives may have been rezoned into different electoral districts.
To have a clearer understanding of the situation the following details could be of help as you track down your relatives's names on old Electoral Rolls.
If your library has free access to online genealogy websites you can check out the addresses of your relatives up to the year 1980
Current Electoral district
Previous Electoral Districts and names
Electoral Districts change over the years
Evelyn and Mornington
Croydon (to 1976)
Silvan (from 1976)
1984-(redistributions in 1989, 1994 and 2003)
Information supplied by Senior Information and Research Officer of the Victorian Electoral Commission