Text Autoflow creates unwanted text frames after I changed Parents to Primary Text Frames

          I made the mistake of starting without Primary Text Frames. I have 400 pages. I must change the text margins. From another conversation on this topic the forum, I am trying to follow Willi Adelberger's solution, although he suggested going to one (1)  page, I am down to page 50. He did not mention autoflow either way.

         I don't want to delete all the pages, but I did delete just to the first 50, as my first 50 pages have 40 non-threaded text boxes, and it would be a lot of cutting and pasting to save the non-threaded items to a spare documennt. I would do that, however, yet, starting at p. 50, the autoflow doesn't work, so why should I expect autoflow to work on p. 1 only?

Or did Mr. Adelberger not mean with autoflow?

         As per other conversations, I have new parents, with linked left and right pages, all with Primary Text Frames, none with text. It works for placing one page, (p. 51, then page 52.) The newly placed text is on one Primary Text Frame  alone with the new correct  margins, and no extra text frame. All is well.  But not with Autoflow. Then I get a second text frame again, a non-primary one and the Primary Text Frame does not have the text, but the non-primary one has the text all of sudden. Why does Autoflow create the unwanted text frame when regular placement does not?

         Clearly somehow because I started with a Non-Primary Text Frame in my now accursed 50 pages, with 350 pages of overset.  Even if I go down to one page as suggested, that one page started as with a Non-primary text frame, so will Autoflow keep doing the same thing?All the way to page 400, with the wrong margins all over again!  Looks like I have to skip Autoflow to fix this, and place all 350 pages one at at time, unless I hear otherwise.