Many D-Link products are manufactured in multiple hardware versions. These different versions of the same product are identifiable via the serial number label which indicate the hardware version: A1, A2, A3 ... Ai, B1 B2, B3 ... Bi, C1, C2, C3 ... Ci. In some instances firmware is released for specific hardware versions, while in other instances, one firmware version is deemed compatible with all hardware versions. An extreme example of this dependency is the DIR-615 (see TSD site), which I raise because I own this particular router.
From what I've seen over the years, hardware changes have included improved/smaller power supplies, new components to eliminate latent defects, and other improvements. There are cases where substantive differences in competing hardware versions resulted in hardware specific firmware.
In some cases hardware version A1 is only sold in the US, while hardware version A2 is only sold in EU. In other instances, the same hardware version is available globally. If you visit the D-Link China site (TSD), you will find firmware versions for specific regions and firmware for specific hardware versions. Again, the number of firmware and hardware versions and compatibilities vary depending on the D-Link product.
Rather than dissect each product separately, and to protect the best interests of the average consumer, we've been casting the general statement to make sure the firmware version matches the hardware version (where applicable). The easiest way to communicate this message is to encourage product owners to download firmware from the region where they purchased their product.
In the case of the DNS-320L, firmware v1.02x does contain actual software defects, which for that reason alone should be enough to avoid installing this particular firmware version on any DNS-320L.