I sort of doubt that James Brady died any earlier than he normally would have - he was overweight all those years ago. I think they’re reaching for their own agenda.
Chances are, I most likely will die earlier than most thanks to that VC bullet - tends to to throw off blood clots periodically. I count each new day as a gift.
If he died from an infected pressure ulcer, or a deep vein thrombosis leading to a pulmonary embolism, or pneumonia because of limited lung expansion, you might make the case that the crippling injury he suffered was the cause of his death.