We Never Know
No Slack
You weren't referring to studies. Rather, you were referring to what cigarette packages didn't say on them.
I actually wrote a meta-analytical paper on this topic a few years back. Of course I can't find it now. But what I found was that very early studies on the subject were lacking in a number of areas.
What I (and others) found was that the number one predictor of violent and/or aggressive behaviour in adolescents was violence in their direct and surrounding environment. Like watching their father hit their mother. Like experiencing gun violence. Like being physically abused.
Why weren't the then warnings on them years ok?
Put it together.