%%They are always basically at the same price at the same time, as any difference gets arbitraged away.
I did see some longer lasting difference, but that was only during non functional markets, ie. no liquidity in ADR / main market, prior to special corporate action, or very hard to borrow during short squeeze.
Of course if you look at daily closes they are different, as they are at different times. Also check out currency fluctuations.
Stock can be flat and ADR up 1% if $ weakens 1%.
arbitrage exists only if there is overlapping trading hours.They are always basically at the same price at the same time, as any difference gets arbitraged away.