John,
We built the spare holes at Kingston Heath,Metro and Victoria.
Metro and KH built theirs because over a few years they were regressing greens. Metro's hole was a restored hole lost in the 1960s. KH played temporary greens on the 4s and 5s but there was no way to make them on the short holes. We are redoing the 19th how - moving the green a little to the left. Given it's now a part of the tournament course it need to be a better hole - something close to the quality of the other three.
Victoria built their to double as a practice chipping area and it's been in play all year because they are redoing the driveway and car park - and with the opening hole playing along the driveway it was deemed to be unsafe.
Woodlands,Royal Melbourne and Yarra Yarra also have spares - although they rarely seem to be in play - not compared with the other three anyway.