I have to admit I missed a few hundred out of about 18k PDFs. I didn't keep track of which ones I archived on my initial pass, so I need to rerun the whole script which takes about a week with Web Archive's rate limit, so I've just been putting it off. I was also thinking people who visit them can click the "archive" button in cases it's not yet archived to crowdsource the effort, like you seem to have done.