Ann: Investor Presentation - Nova Positioned for Growth, page-84

You said that "they deem it is necessary". The question is When it deems as necessary? It looks like that they do not know how to use the buyback effectively instead they used it to buy own shares at a lower price. In this case, a buyback is a waste of effort like pouring water from sea to a sand hole in the beach. Actually, they should proactively use the buyback mechanism to maintain the share price so investors feel confident about the company.

Unlike in the US, a buyback can be put as Treasury stock, and recorded in the balance sheet. Buyback in the US will not reduce shares outstanding. Buyback is used as a signal to investors that the company is confident in the future prospects of the company. They buy back the shares because they believe the share price is undervalued due to temporary market sentiment.

So the US companies  buy back the shares at a lower price and then could be sold again at higher price when the market sentiment has improved.

In Australia, when the company does a buy back, the shares must be cancelled and it can not be sold back on the market. Yes, in Australia, the buyback will reduce shares outstanding but not in the US.