I maintain two web sites that date back to 2003. They are still very active (thousands to tens of thousands of uniques per day), but I and my users have noticed that only the more recent content (2012+) shows up in Google. In a way I’m had to hear that Google is delisting the older content because I thought I was doing something wrong. But it’s still frustrating for my visitors because every few months I get a messag…
Is it possible to check your access logs, see if google how much google, others are spidering? I know very little about google's SOP, but had the impression they periodically rescan stuff.
Duck Duck Go finds it and shows it. According to the logs, Google spiders it, but chooses not to show it.