Shared documents library of PDFs not found by search, but no apparent errors on them when I search the current crawl log

I have a SP 2010 farm. I have verified that crawling is taking place. On one particular site collection, I have found a shared doc library which, when searching just this library, returns no results.

The library contains PDFs.

Those PDFs are readable by all staff.

The crawl logs do not show any error or warning on the documents.

Now, the documents are visio charts with text written out as PDFs. Should I be seeing search hits on these?

If I know for certain that PDFs are being indexed elsewhere on this site collection, and the permissions look okay, and the documents are not particularly large, does anyone else have other ideas on why the search is not returning things that it should be?

Thank you!