My super ikonta iv does not allow the user to ability to advance using the window. Each advance/spool on is predetermined and locks in place with counter. The window in the back is to check if there is film in camera only, and not to place frames.

It's been documented online quite a bit that this camera needs about a 2inch section of backing paper taped to leader to have consistent spacing. I do it and it works fine, but can be a hassle if you shoot more than one medium format camera in the bag. You also have to plan ahead with the tape and rubber band/ use 120 canisters.