OK, in just a moment I shall be including in my next post a complete dataset of bad links. There are going to be both false positives and false negatives. The false negative rate is not something I can do anything I can do very much about technologically, but will be fairly low [in theory I can test for various silent error 200 redirects and the like, but it's probably more trouble than it's worth. There won't be many]. We'll just deal with those few as and when we stumble across them. As for the false positives, these are something we are going to have to test for manually from the small dataset.
There are a number of different results. "Checking..." basically means connection timeout. For the most part with these ones, we're not just looking at a bad link, we're looking at the whole website having gone down over the years, the domain not having been renewed, or whatever. Most of these are going to be legitimately broken links. Websites marked as "secure" are either internal links (for some reasons I don't understand), or external secure links. These could not be properly tested by the tool I was using, so most are going to be false positives. Error codes 5xx are likely to be completely broken servers, so are likely to be legitimate. The 4xx errors are likely to mean that just the link has changed but website still active. There should be no false positives in the 404 errors (in theory - in practice a good webpage could return 404, although this is very unlikely), although a typo in the URL whilst copying into the table could cause a 404 whilst the intended destination is still active. 3xx errors will be mixed - most will be redirecting to the homepage or generic support portal, a few may be usefully redirected.
There's a total of 687 entries in the list overall, which is a bit of a pain. I'll see what I can do shortly to whittle it down a little by taking out all of the obvious false positives. Then we'll have to share it out & start opening them all up & looking for alternatives
If we work on this as a team, it may be worthwhile starting an Office Online or similar document. I'll see what I can get knocked up. For now though, this is just a quick data dump - I'll see if I can make it better before we set to.
Richard