ECCNs change over time, as what was once state of the art eventually becomes commonplace. So, an ECCN may change over the life of a long running product, and even more by the time it reaches the used market. Over time it becomes less interesting for a manufacturer to put the effort into getting an updated an ECCN rating, so anything you find on their site might be old, and more restrictive than necessary. I'm not clear how you get something current.