Yeah, I don't understand "First Strike" when a coin was sold out in 3 minutes. So each and every one of them should be first strike. But one needs to send an unopened shipping box or whatever to get that label (at least from the few I've looked at).
Most overused word: "Unique" Dummies: That means that there is exactly one of them. Penny: A British coin. Regarding Sliders: This was a common term used in the 60's & 70's: simply meant that they were "almost" unc, usually used in reference to high end AU coins. I believe it came from old time collections that were kept in coin cabinets. Each coin had a space for it. When you opened & closed the drawer the coin would slide around and eventually would show some friction on the high points. They were once unc, but developed some 'wear' from sliding around in the tray. But, oh so close to unc.