Talking to Chas at Stern he implied that they are only covered by Stern for the original owner for 6 months. But when we had one go bad on a GB as a second owner and 1 year after the original owner bought it, our distributor hooked us up.
Now, that may be our only 'get out of jail free card' as I don't think they'll keep doing that every time a node board goes bad in the same game. If you have multiple board failures over time you may only get a replacement once. That's the scary part is if people keep having multiple node board failures. That will get very pricey.