I've got a couple of bottles of OFBIB (one is a fifth, the other is a handle) that have tax stamps, both of which indicate that they were distilled in '71 and bottled in '77.
The label says "This whiskey is 5 years old", so the tax stamp contradicts that a tiny bit.
But my real question is, is it possible that this whiskey is older than the tax stamp indicates? It certainly tastes older than 6 years. I hear stories of glut whiskey, and I wonder if the tax stamp could have been fudged for one reason or another.