This is what I think:
The machine does not recognise the player by membership card BUT the casino management CAN.
The casino choose the winner by reading his/her details thru the server and decide wheather or not to release the BIG jackpot prize to the player.
Machines located at corner/pathway or code number ends with 1 stands a higher chance to hit the jackpot. I have seen this many many times. The machine that I won the jackpot too located at corner.
REASON: Corner/pathway machine has more room to accommodate crowd, casino simply wants to tell more people that they are really giving away prizes.
Well I've yet to witness any of this or to hit the big jackpot myself
BUT I do find that a couple of the End/Corner slots that I like playing seem most-of-the-time 'luckier or paying-out'
So HOPE that whenever these are free/available for me to play the management will NOT reverse (choose not to release/award) the jackpot SHOULD such be lucky enough to 'drop' when I'm playing :p
BTW - have found a couple of "2nd-position from end" slots BETTER than the end corner slots
eg Sinbad Money2Burn & a row of PP slots