Years ago, I had four sites in the same niche with similar content. 9 months ago, I shutdown three of the websites and parked the domains, leaving me with just one website in this niche.
Some of the content from the shutdown websites was good and I would like to republish it on my one remaining website. Is it "safe" to re-use the content from the shutdown websites and republish it on the one remaining site? Or does Google remember that it once lived on a different domain and therefor it's duplicate content (even though the original no longer exists)? Anyone have experience with this?
If the content is no longer actively served, and then it re-appears on a different domain, it's not duplicate. I'm sure Google has extensive historical data - but we don't know how much or how they use that data. All iinds of things are "possible".
I can tell you from experience that if old content that is gone is now put up at a new URL, that also does not cause ranking issue.