Rob, your general outline of the patent/trademark law is correct as I understand it.

I'm not a lawyer but non-propagation agreements are difficult to enforce and thats why commercial breeders usually only use them for limited circulation to testers they personally are interacting with. Greenmantle is the only nursery that uses them for heirloom varieties so I assume they are the place you are talking about. If I were to say pick up some of their varieties in a pile I found at a random swap meet, Greenmantle has no recourse unless they could hire a detective and track down who brought them to the swap. They certainly can't go after me, I have not violated the agreement since I didn't sign it. That is why non-propagation agreements are not very powerful legal tools.

My general opinion of Greenmantle is low, not only for their arm-twisting tactics on these old varieties which they have no legal ownership of, but for selling bench grafts that often die. They sent me a benchgraft with the scraggliest rootstock you have ever seen, it had only one thread of a root. Of course it died. Then when I asked for a refund they got all huffy and said I overwatered it (I didn't water it at all, it was spring and plenty moist). They did eventually refund my money.

Scott

Plant patents are good for 20 years from filing. You need permission to propagate any patented plant still covered by a viable patent. Once expired anyone can propagate without permission or paying a license fee (and royalties).

Royalties typically range form 50 cents to $4, with $1-$1.50 typical. Reasonable. When you buy a patented plant the license royalty has already been added.
You need to work out an agreement with the license holder (can be painful for small business) to sell their patented tree grafted.
Patent check:
If you use the numeric search plant patents are preceded by PP and are 5 numerical digits. So if a provider only lists four digits, like pat. 9890, you would enter PP09890.
Note as of this posting, any patent filed Feb. 22, 1994 or older has expired.

Trademarks are good for life: Pluot is a trademarked name (by Zaiger), plumcot is not (coined by Luther Burbank), yet both refer to plum x apricot crosses. Only the Zaigers (or those who license the privilege, ie, DWN and those who buy trees from them) can designate their plum x apricot trees pluots.

http://www.freepatentsonline.com/

Here is a link that might be useful: US Patent Check

Oooops, I guess math is hard: "....any patent filed Feb. 22, 1994 or older has expired...."

I should have said 1993, not 1994. Bad dog.