Is the serial number also inside the unit

I am asking this because I returned my Blackberry Playbook to their repair because it wouldn't run. They said it was liquid damage and not covered by warrantee. They returned it to me. Now the unit had set in my car for several days without being charged. It had not come into contact with any liquid. I took it into the house and charged it. Tried it didn't come on. then was sent to the repair centre. They said "Tech has found 5 red LDI -- visible liquid damage on the back cover, motherboard, battery, WIFI antenna, audio jack, speakers, and the bluetooth, GPS & WIFI cable boards. Also, the HDMI port is damaged and the USB port is not functioning". I can not understand how this can be. No liquids touched it. Could you explain.

John