Dmtiry,
One way you can find these may be the publication reports.
For a slicker way if you publish some metadata like publishing date (or a revision index set in content class templates) to a DS attribute you could have a search or target DynaMent to identify old contents. With a full site republish you could identify contents that are likely to be orphaned.
On a side note having the metadata that the WSG Best Practice Project sample project uses in content attributes can facilitate a lot of interesting use cases. These include:
page id, page guid, publication date, creation date, parent page guid.
Best,
Tim
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