In all of those 17,500 links (yes - that many) there are some links to collections from Hathitrust, which I have written about before, and which is a partnership of academic and research institutions offering collections with millions of pages that can be searched for free. It is similar to Google Books in function. Today, while taking another look at the main Hathitrust site, I searched the catalog for newspapers and found 189 newspaper titles in the collection. I know for sure that all of the newspaper titles available are not in the Newspaper Research Links page (yet).
The other observation is that about 70% are from the U.S. and a majority are from the 1700s and 1800s.
If you are researching older newspaper titles, I would advise you to check out the following link:
You will be presented with the 189 titles and on the left sidebar you can further hone in by location, decade, language, etc.
Many of the titles are short- runs (i.e., not many years) but it may be worth your time to search these "older" collections, which may not be online anywhere else.