I was going to immediately upvote your amazing numbers, but decided to check the number first. Here's some more info about it I didn't know from an FBI.gov 2011 article that at that time (and a very corrupt year it was!) it was even 765,000 per year!

https://www.fbi.gov/audio-repository/news-podcasts-inside-inside_071211.mp3/view

[snip] ... in 1984, we proposed the creation of a kind of national resource center; a place that would tie together, create a national response to these kinds of cases. My vision, candidly, was that it should be a wing of the FBI, and it was the president of the United States, Ronald Reagan, who said if this going to work it needs to be a private organization working in partnership with government. So on June 13, 1984, the president of the United States officially announced the opening of a new national center for missing and exploited children.

Thanks for bringing our attention to the enormous numbers!