Kohler NPT 3/8 in. Annealed Vertical Tube Angle Supply with Stop

I had this valve installed as a part of our Master Bath complete remodel in 2017. No issues until now. I needed to replace some of the seals in the toilet take to eliminate water waste and am in the process of completing this now. In preparing to replace the tank parts I shut the water off using this valve and noticed that the fill valve still allow a drip flow of water to still enter the tank - not completely shut off. I shut the main water off and removed the supply line and the valve stem to check for debris and didn't notice any. I was intrigued to see that there didn't seem to be a washer inside the valve to help seal the water flow. Instead I found a smooth machined circular "wedge" with a finished surface that must be contacting a matching inlet edge to provide the mechanics to stop the water flow. It seems that this approach is not 100% effective in shutting the water off when closing the shut off valve completely. Is this accurate? I thought I would find a broken rubber washer but it doesn't look like the valve has a internal washer in its design. It is possible to do repairs quickly with the continual drip that comes from the valve when closed but this seems odd. Can you please advise?