I'm not sure there is a real answer. It may be that ADR and regular shares are readily changable on some markets.
One number I think I remember if that the At The Market program (part of what was just sold out back in Oct.) was described as "50,000,000 shares to be stored #$%$000,000 ADR" or something like that. It sounded like some kind of bank account system so I'd suspect there's ways to change that balance as long as you maintain enough liquidity.
Basically I expect the brokerage houses in each market keep running the arbitrages back and forth as the relationship between the markets fluctuate.
Thanks. That number is probably the PRAN Aussie shares a few months back (they have approximately 340M now). American ADRs represent ten PRAN shares (Aussie). What I'm trying to determine is how many ADRs are authorized for USA trading. Is it ALL the 34M or some predetermined portion? I asked the American bank that controls the ADRs but they said the answer is (may be) proprietary and I'd have to ask PRAN investor relations. PRAN didn't reply.
so if this is the case then why we have two different tickers PBT and PRAN, I think this 308m is only in US otherwise it is hard to know the actual value of the share where in ASX it is being traded 1/10 price.