I disagree. How can they know there will be vacancies if no one has accepted their offers yet? Remember that list was released at 9pm when offers went out. It's just conjecture, in my opinion.
They can issue less offers than places.
However, according to UAC:
"A letter ‘V’ shown in brackets after the cut-off indicates that some places
may be available in the
Early February Round. Vacancies could also arise in some courses not marked ‘V’. This will not be
known until after acceptances to Main Round offers have been received and
no guarantee is given that
further offers will be made." (emphasis added)
So you're right, (V) means they think there will probably be vacancies, not that there definitely will be.
My guess is that the unis are able to estimate - they know what their acceptance rate is generally like, they know how many places they have and how many people have applied. It may surprise you, but admission is not an entirely automated process - admissions offices still have to employ people to assess UAC applications, so they have an idea what's going on.
