...but that's the problem with simple anecdotes from veteran keepers. They are unreliable and biased.
This whole conversation is "unreliable and biased." There have been no studies of average lifespan of wild snakes vs. captive bred ones. There have been no studies on which for sources are better or if any are nutritionally complete.

Sometimes "simple anecdotes from veteran keepers" is all the information there is to draw conclusions from. If you want to disregard them, that's your prerogative. But I've always thought that was the idea behind forums such as this one - for people to share their experiences.