We get this question a lot. Quite a bit more than expected.
Our inventory system is live. That means, if we have 3 of that product in stock, when you order one, it goes down to 2, etc. Thus, if you placed an order for an in-stock item, then it was in stock at the time. When you go back later on, sometimes even just a few hours later - it could be out of stock! We do this because if we didn't track our inventory, we'd oversell on things CONSTANTLY, as orders come in far faster than we can watch, sitting at a computer.
Now, that is not to say our system is perfect. From time to time we still encounter inventory glitches, which we'll work with people on when they occur. We do our level best, but we're a small shop!