The “Google powered search box” is a “Google Custom Search” — a Google search restricted to the BBS site — so it relies on the information collected by Google’s “web crawlers” which collect the information for the Google indexes. The crawlers only visit sites periodically, so sometimes Google’s information lags behind what actually exists on the website. From time to time a new or improved BBS INFORMATION file will be uploaded and Google will take a few weeks to catch up with it, so until that happens it will not appear in the results of your search.
When you search for text in a pdf file, you are searching for “text behind the image”: the pages of the old BBS issues were scanned as images, then special software performed “Optical Character Recognition” (OCR) on the image to produce searchable text. The original scans and OCR were done several years ago, since when OCR technology has improved greatly. The BBS is therefore repeating the OCR process to create more accurate text, and the old pdf files are gradually being replaced by new ones — and eventually Google will catch up with this process. OCR of the PDF files is currently being done with Abbyy FineReader 11.
Visiting webmasters might like to know that in this WordPress site, the Google-powered search box is provided by a Plugin called “Google Custom Search” (published by Little Handy Tips), and the resulting php code is placed on the page thanks to a plugin called “Allow PHP in Posts and Pages” (published by HitReach).