Photo stream on iMac, iPhone, iPad and Apple TV

The photostream on all 4 devices are different. The photo stream in photos on my iMac is only showing a select few photos from nov until now. How do I get them all the same? All of my devices are linked and set up for sharing.

Also, the screen saver on my apple TV is set for my photo stream. It is showing different pictures than those on my iMac and iPhone. Where is it pulling pictures from?

I would like to have all devices have the same photo stream.

Thank you,