To start with, its a good idea to assemble and test each individually so you know each Trellis works individually.
Each Trellis tile must have a unique address. You can set the addresses on the back of each panel using a little solder over the address jumpers.
The HT16K33 driver chip on the Trellis has a default I2C address of 0x70. Since each device on an I2C bus must have a unique address, its important to avoid collisions or you'll get a lot of strange responses from your electronic devices!
Luckily, the HT16K33 has 3 address adjust pins, so that the address can be changed. Each pin changes one binary bit of the address, so you can set the address to any of the following (in hex) 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77
The panels don't have to have consecutive address #'s, they just have to be unique.
For example, this Trellis has A0 shorted, the address is 0x71