> Those patents would have been issued in the 70s and long since expired.
This makes sense if you're talking about individual patents, but often patents are interlinked, and with a "priority date" of a "key patent", subsequent patents can be filed and granted that effectively extend this window... these constitute a specific "patent portfolio".
This makes sense if you're talking about individual patents, but often patents are interlinked, and with a "priority date" of a "key patent", subsequent patents can be filed and granted that effectively extend this window... these constitute a specific "patent portfolio".