Based on my research and posts read on this list and others I will try to answer your question. To those who may know more pease pipe up.
The Land Yacht plate is on most of the 60"s and 70's Airstreams. It was used as a marketing method. The Overlander is the actual model name. If you look on sites like
they will list each year and the models desiginated by name. The name also was an desiginator of length in most cases. I have not looked at your online profile but I would bet money your trailer is a 27 ft model. The international name is also used thru the 60's and 70's but I do not know why. My best guess is that again it was a marketing tool, to say that you can travel to other countries because your trailer was designed to be used Internationally???
Hope this helps, and welcome the forum.