That is strong evidence that GMO does not have observable risks within 10-20 years of adoption, but it is considerably weaker evidence about what GMO adoption looks like after 30, 40, 50 years or a lifetime.
You can replace "GMO" in this sentence with a lot of things. For example, "kiwi". Or "cell phone".
Yes, I would agree. And I completely assent that 20 years of evincible safety can be extrapolated into "long term" (however you define that) safety more than 10 years could be. My only position in saying the above is to highlight that "It's seemed safe so far" doesn't necessarily prove that to be safe in perpetuity.
Surely you are not arguing that 20 years is the magic asymptote at which safety rises to infinity?
Basically: How does one pursue the truth when direct engagement with evidence is infeasible?
I came to this question while discussing GMO labeling. In this case I am obviously not in a position to experiment for myself, but furthermore: I do not have the time to build up the bank of background understanding to engage vigorously with the study results themselves. I can look at them with a decent secondary education's understanding of experimental method, genetics, and biology, but that is the extent of it.
In this situation I usually find myself reduced to weighing the proclamations of authorities: