One of the lessons I have learned about the germination of tree peony seeds is to never move them during the summer, or when they are still growing because I lost a bunch of them however I still have well more than enough for myself since I started with a decent number of seeds. I lost a large plant as well as many seedlings, and found out later that the only real good time to transplant them is around now when they are fairly dormant.
Hundreds of seeds have since been planted and should be sprouting next spring or the following one, and I have also done a plant trade with cricket hill gardens to obtain a few more species of tree peonies which are now planted.
Here's my updated thread on these guys.
Steve's garden: Update on the tree peonies seedlings and grafted plants