Honestly, when it's just 2 regions and not even a city, is there really any notion of a 'realm' merger? Coria didn't even have a capital, so IMHO it wasn't even a realm anymore.
I'm inclined to agree with this to an extent. Coria was not a viable realm anymore. Its only city was taken by Silnaria. At that point I'm not convinced you can call it a realm merger in the sense of the type of transaction we're trying to discourage with that rule.
In addition, Lothruin revolted and joined Tara; it wasn't an action intentionally undertaken by the lord of Lothruin, but a result of game mechanics.
