Any lawyers can correct me if I am wrong, but the law in the US and probably Canada focuses on intent. If it was found that a girl that claimed she was 18 was not and the company had to pull her films because they found out her age later and she forged her birth certificate, etc., I very much doubt that they would go after anybody who viewed or downloaded it, because the law involves the original intent of the accused. No one in that situation intended to view the porn because they thought one of the subjects was underaged.
It is pretty obvious that the unfortunate children in child porn are very underaged. The perverted guys who seek child porn seek children, not 17 year olds who look like fully developed women.
Traci Lords was very mature for her age. She fooled many actors, directors and producers of porn. No person in the US was arrested for possessing her porn. From what I remembered, some directors faced legal problems. Her videos were immediately removed from all video shops and destroyed.