What you have is not an error .It's from a "greased fill die" . Generally, missing digits or mint marks on modern coins are due to filled die errors where dirt, grease or debris fills the recesses of a die not allowing the number or mark to strike up. The metal from the blank can’t flow into that area to receive the impression. So, there is no added Value.
The first one is known as a greaser. It was struck through grease so it appears weak or non existent in a limited area. I don't see anything but wear on the second one. Welcome to CT.
Filled dies ARE considered errors. But you're correct, most are considered minor and don't add much if any additional value. http://www.error-ref.com/?s=struck+through+grease
Always show both sides of a coin. If the second one is a 2005 Kansas, it's the familiar "In God We Rust" error - also a grease-fill die.
Greasers are indeed errors. They did occur in the minting process. The additional value depends on the level of obscurity. Say you have a nickel greaser missing a single letter. Not much if anything there. Then you have the same date nickel missing the entire moto. That would give that coin a premium, although small,but a premium. Say around $5-10.
