When you mix paint for a living, it's really common to have people want you to make more paint from stuff they had gotten in the past. Companies change lines and formulas all the time, so after a few years, you can easily tell when something is old. You wouldn't believe how many people say "I got this a few months ago" and the sticker said 2014 or something like that. I had a guy had a label from over ten years ago, and furiously denied that it was old when I mentioned it. It wasn't even an issue, he just wanted more, he wasn't even trying to whine for a freebie.