The only discipline you would need to report or that they should be asking about is progressive discipline leading up to your recent termination for the specific thing you were terminated for. In other words, if you received a write up for being tardy three years ago, or for just about anything, really, it isn't going to be relevant to their coming in and firing you now. You weren't even told WHY you were being terminated anyway. Most warnings are considered beside the point after about a year anyhow. And you can't warn someone and then three years later fire them for that reason and expect to be found to have provided them progressive discipline.
Yes, if you're caught up in a lie, it makes you less believable. But in that case, if they came up with a three year old warning, nobody's going to pay much attention to it anyhow. You don't have to shoot yourself in the foot by trying to tell them just everything in the world. The omission of an irrelevant warning isn't going to damn you.
I seldom see anyone so determined to self sabotage and try to convince themselves they're going to be denied unemployment. Why don't you wait and see how it turns out?