Thanks, Mark. That's very helpful. There's one scenario you didn't cover directly. (The one I need!) There are people who have Paratext, but they want to typeset something that they don't have a project for. I'm thinking, for example, of Language Technology training, where you want to typeset a book for practice, but you don't have a Paratext project for the book to typeset. In that case, it appears that you can create a unique sub-folder under C:\My Paratext 9 Projects\, and as long as there is at least one *.sfm file in the folder, PTXprint will make that folder available as a valid Project ID.
Does that sound correct? Seems to work for me... and I'm able to do typesetting of my sample book.
One note about the training video. You create a ScriptureProjects folder under C:\Data at the beginning of the video. When you create a folder for SFM files in the last section of the video, you put it in C:\Documents\ScriptureProjects. None of those other projects that you loaded (DBL, etc.) are there in that folder, so it seems clear that that is not the active PTXprint data folder. I'm guessing you already had a copy of the SFM folder in C:\Data\ScriptureProjectSo and that's why it showed up in the PTXprint project list. If that's where PTXprint is looking for projects, it's not going to be able to find the folder you put in Documents. Not a big deal, but could confuse some people - something to fix in the next version of the video...
Thanks for all your good work! Jeff