Custom Armor values not adding?

I have given myself netherite armor but I changed the values of the armor, knockback resistance, and armor toughness  for all the pieces. I made sure to put it on the correct armor piece like leggings have when on legs etc. When I put on one piece of armor it works correctly but when a 2nd piece gets put on it gets rid of the armor that the first piece adds and replaces it with the newest piece put on for example look at the pictures
I get 2 armor bars with these boots which is correct
https://i.thick.at/KkntHPRm.png
But when I put on these leggings 
https://i.thick.at/hX8Uy5WG.png
I just go to 3 and a half armor bars which is what the leggings should give and if I take the leggings off I have 0 armor bars with the boots on. Any idea what is causing the armor pieces to override each others stats?