@dobey I am not here to argue. I was just trying to help using the information I had being in North America and having to deal with carriers dropping bands. The problem is even bigger as the bands are dropped regionally so for one person it may work and for another it will not. It is often that low usage areas keep their old bands longer as they are not seen as worth the cost to upgrade the towers in those areas but busy places get new hardware and lose support sooner.
We are both correct. If I go on eBay and search "Nexus 5" I will not only get one compatible with US carriers because there are at least two model variations of nexus 5 so you can not just say that the Nexus 5 is compatible either. But as you say if you get a specific version of the Nexus 5 it is compatible in the US on certain carriers for a limited time.