For combo cards (GV1120/1240/1480), only v1.02/v2.00 and A cards are stackable.
Note: Only same model can be stacked.
For example, GV800B can stack with another GV800B, but not GV650B.
Note: Only same hardware version can be stacked.
For example, GV800B can stack with another GV800B, but not GV800A.
Refer to Hardware & Software Compatibility Chart below for more details:
In order to find your version number, you need to remove the card from your computer and look for the numbers highlighted in the picture below. Always power down and disconnect your computer from its power source before attempting to remove any component!