i have spent time on track records over the years and generally several factors have an impact. weight carried. track conditions,
e.g. rarely should there be fast tracks due to damage to horses. and also i am suspicious that distances might be vague at times. i recall years ago races at flemington, moonee valley etc. were always exact distances but over the past 10-15 years theres 1409metres and all that sort of thing. some distances were unassailable for many years until horses like vo rogue arrived on the scene and broke most records.
on a true weight and distance measure the randwick 1600 record should almost be impossible to beat due to time set in an epsom handicap a few years ago.
if it is i would wonder particularly if by a lesser type of horse.