I still fail to see why they even would store Chang's money in a locker in the first place. It has no obvious benefit, and considering he was driving around in the exact truck that was being searched for until he got to the station it was even somewhat of a risk, albeit a small one due to how short that trip was.
You could argue that it is better to not keep all the money in one place in case Kaiji and Mario were discovered, but then keeping 75% of the money there wouldn't make sense either. The whole locker idea seems to be there just so this problem could arise.