"Could a board fail after 12 and 1/2 months?"
Any electrical component can fail at any time. It's not likely but it's more than possible.
"Is this considered product defect which could affect all the iPhone series made during the same period/location?"
I've had my iPhone 5 for just over a year and it's not failed. I know others who have the same model for a similar amount of time and they've not failed either. Then again I know some iPhone 5S owners who've owned theirs for only a few months and they have failed. None of this in my opinion means these are product defects.