My father just died from lung cancer at 87. It came as a huge surprise, probably masked by other health issues he was having, and was discovered well into stage

My father just died from lung cancer at 87. It came as a huge surprise, probably masked by other health issues he was having, and was discovered well into stage-4. He was given 6 months, and made it about 4. Watching him deteriorate into a world of pain and eventual confusion is an intensity of human experience I would not wish on anybody going through it first or secondhand. That being said my family has started to wonder, "when did he first get sick?" as he seemed relatively well until early last year -- other than his other conditions. The best we can come up with is "about a year ago". But looking at this it may have much much earlier. It probably wouldn't have changed the treatment or outcome, 87 is a hell of a run, but from an objective point of view it's very interesting to try to understand when this terrible thing first saw its genesis in him.