Ralph,
Danke.
I will probably not worry too much about the Thurn & Taxis exception until I have more items that require that knowledge. For now, I have my hands full trying to figure out letter mail 1850-1875 in Western Europe at the basic to intermediate levels.
Recently published an article with the Postal History Society (US) on a series of letters to Amsterdam from various parts of Europe. Working on a second article looking at Swiss/French mail exchange. So, that is where the detail effort is going right now. Nothing groundbreaking, I am sure. But, basic knowledge of the workings of foreign mail outside of US interactions needs more exposure in the US, so I am hoping to provide some of that.
The problem is that I very much want to get things exactly correct, but I know I have many gaps in knowledge.
Rob