In answer to your first question, the amount of stock available to purchase on the AU market is equal to all issued shares minus any shares held by institutions holding the stock for ADRs. The institution cannot effectively sell the SSN shares which are held on behalf of the US ADR holders so obviously that stock cannot be considered available for trading in AU without ADRs first being cancelled.
If new ADRs are to be issued for release into the US market then the institution must first purchase the SSN shares in the AU market during the AU trading day, or borrow the stock from another institution. Once they hold the required securities they can have more ADRs issued which they can onsell in the US market. If they borrow the stock however they will have to cover their position by buying the stock from somewhere. This could be done by buying US ADRs to cover their short position, or by buying shares on the AU market.
Trading overnight in the US market can therefore result in additional buy or sell orders in the AU market.
I hope I understood your question correctly TCG.
SSN Price at posting:
5.9¢ Sentiment: Buy Disclosure: Held