Nice examples Jerry. Your last postcard with only 5 Pfennig instead of 6 - it could be that it was cheaper because of being a business postcard and not a private postcard. It's called a "Drucksache" or as you say "Printed Matter" which is always a bit cheaper.
You talk about the cancellation - exactly right, that's what I meant too, but I missed that word. I only knew stamp for Briefmarke and also stamp for Stempel. Cancellation is much better.
By the way, unused original stamps from the 3td Reich are very common, cheap and available in great numbers.
Kind regards
Robert
