I'm late to the post but I was searching for this myself today. No need to save the untitled project when you're done, as it should just have the opening and closing titles left. The advantage of "cutting" each selection, is that you don't get lost as to what topics you have and haven't done as you go through. On the last one, I also split the selection just before the closing titles. Then just simply repeat for the number of topics you have in the full video.
Lastly, I save the project and export it as an MP4. Then I open a short form closing title "template" project I've created (all my short form closing titles are basically the same), select all, copy, jump back to the topic project, and paste. Then I jump back to the untitled project, split the video at the end of the opening titles, when the first corner annotation comes up, skip through to when the next one comes up, split it again, then cut (not copy) the selection, jump back to the topic video project, paste it, and then add a quick fade in and out to the clip, to avoid any overlaps. I then open a short form opening title "template" project I've created, adjust the title accordingly, and do a "Save As" as a new project, named appropriately to the first topic of the full length video. To make the shorter topic videos, I open an untitled project, and import the full length video. Once the annotations are applied, I export the full length video - which is my initial finished product. I place markers first, while I'm editing, with the topics on, so it's easy when I go back through to do the annotations. The way I do it, because I'm splitting long videos up into topics, is I place the title of each topic as it starts, as an annotation in the top left corner of the screen, after I've edited the full length video footage, and created the opening and closing titles.