The modification between the two versions is very minor. The only way to tell the difference is by looking at the strip of metal (or lack thereof) that goes between the I/O panel and the first PCI slot. As you can see in the picture the new version lacks this strip of metal.
A new part number was not issued for this change, and the box has not been modified in any way between the two versions. This means that, unfortunately there is no way to tell which version you have just by looking at the box. Only the initial first shipment (5000 pieces) of the case had the first slot issue. Since then tens of thousands of new units have been shipped with the correction, starting in mid December. While there still are some of the 5000 original units out in the retail channel, the majority of Nine Hundreds in existence today feature the revision.
The good side is, only those motherboards that have their graphics card in the top slot and use DVI connectors are affected, which is a small percentage, as most motherboards place their graphics card slots one or two town from the top.
If you do happen to run into this issue, please contact Antec customer support at customersupport@antec.com or Europe.customersupport@antec.com and they will provide you with a solution.