This article contains older and outdated Linux and Android releases for A20-SOM and A20-SOM-EVB. There are also older build instructions (older image revisions might be used as a reference, for testing purposes, or if you own old hardware revision of the board).
The latest stable release for A20-SOM and A20-SOM-EVB should be found at the main wiki article of the boards HERE
Old Debian releases
Older official images - Debian 8 (Jessie) (not recommended):