Plants with seeds - ?

I have had a couple plants that I harvested recently that have a fair amount of seeds. Thing is I have also harvested a couple plants from the same room with no seeds at all. Think I have some partial hermies that may7 not have pollinated the whole room? I have only been growing regular seeds recently and will not be using feminized seeds anymore. Think this will help?

Check the room and make sure there is no light leaks. Sure way to stress a plant into self pollination.

Yeah, sounds like the plant may have been stressed out and self pollinated. was plant older then others... like havested late?