Length of reign shouldn't matter. It should be number of defences. I don't know why that isn't a record to get accentuated more. A guy can hold a belt for 5,000 days but defend it once a year, so the days held is meaningless.
WWE used to be able to get around this with their fighting champion rule, where if you didn't or couldn't defend your title for 30 days, you'd be stripped, but that fell by the wayside.
I feel it's a good rule of thumb, though, and should be reflected in kayfabe that if you don't defend your title for 30 days, then either your lose the title or your reign length resets back to 0.
