'Personal experience' lends itself to self-report in much the same way that 'observed natural phenomena' does not.
edit: My answer feels incomplete.
Less Jokey Phrasing: Self-report is tacitly accepted for personal experience whereas it is not for observed phenomena.
Not sure how to unpack that further.
You're right in a way. How about self-reporting in instances of herbal drug or homeopathic remedy usage and their benefits, for example. We completely discount such claims everyday. However, self-reporting in cases like this inherently garners more credibility. Why?
Edit: I realize statistically one is far less likely to falsely report sexual assault than to tell the truth, it seems. I do wonder in the recent acceptability, support, empathy, publicity and consequence of accusations of this sort, has the percentage of false reporting grown? The occurrence of false reporting sexual assault is far from 0%, though, too. Moreover, many accusations as of late in the media and elsewhere seem to be of sexual harassment. Do we have any idea how accurate reports of that are?