The sprites, the secret text strings, the debug menus left in the final build—they are all waiting inside those .sgdt files. All you need is the key.
If "SGD" refers to Speech Generating Devices, the viewer feature set would also include: Predefined view settings for view wizard in a draft file sgdt viewer
Even with a dedicated SGDT viewer, you might encounter issues. Here is a troubleshooting table: The sprites, the secret text strings, the debug
It stores a 6-byte value consisting of a 16-bit limit and a 32-bit base address. the secret text strings