Were there two versions of the Nad 304?

Hello, I recently saw a ad on another site that has a 304 for sale. The pics of the rear of the amp showed a plug outlet that you normally find on older gear. I have a 304 without this feature and the plug on mine also has a adapter. When I slid the adapter off it revealed two round posts apparently for some other country other than the US. Do I have a "special" piece of maybe a newer version? It didn't come with papers so I'm a little in the dark here. Inquiring minds want to know. Thanks and good listening.
Sounds like a gray market unit, but that's only a guess.
Could be an international version opposed to a US version. Or is could just be a newer or older one. I've seen this a lot with other gear.

Just to name a couple.... Earlier Rotel 940 CD players have no Coax digital output; later ones do. Some Cambridge Audio gear switched from a fixed power cord to an IEC part-way through the production life. Cambridge has changed remote controls in the past to the same gear. The MSB P1000 Power based went from internal jumpers to change the voltage from 110 to 220, to a switch on the back of the chasis. All of these changes happened without any change in the model number, etc.
Thanks to all that have responded. My guess is that my amp is a Euro version based on the power cord I described. And the beat goes on : )