The corrupted SD card reports are a sign that this system was not completely thought out in the design process. Various methods of success or failure to recover confirm (to me at least) that the SD card hardware cannot always function correctly during a power down situation. The card is known to contain the database of frequencies and zip codes, etc. But it is also being used to store other customer options, state at last power-up, and a variety of other housekeeping information that is used by the main micro controller. In some products that use external cards or EEPROMS, part of the actual software is contained in the card, which might include the country specific setup options, features available in a particular model, etc. Losing that type of information will completely disable a product.
Apparently the unit is constantly reading from and writing to the SD card during normal operation to obtain the customer programming information. Also, a certain amount of information must be written back to the SD card every time the unit is turned off. But, if there is insufficient power available either in the power supply or in a backup battery then a "write" can fail at some indefinite point leaving the card corrupted. If the formatting on the card is corrupted, you get the un-recoverable error message. You should be able to re-format the card in a PC, but re-formatting may not recover your data.
In my opinion the corrupted data problem is not due to dirty card contacts or wrong card manufacturer. As I see it, card corruption in this case is a power-down issue involving insufficient power to the micro controller if it is in the middle of a write to the SD card. Obviously the corruption doesn't happen all the time. That's the nature and the excitement of electronics design.
FF