Even though you didn't cover this topic in particular, it's related - I have asked the same question about 100 times when it comes to a variation in this experiment, and not a single person has even come close to answering it. They don't even try, because I think either they, or I, don't understand the question.

It's a well known fact that if you OBSERVE the photon before it goes into the slit, the wave function collapses. Here's the question that NOBODY has answered: "What do you mean by OBSERVE". In order to OBSERVE a photon, don't you need to interact with it (e.g. measuring the eletronic magnetic energy, shining something on it, etc.????). And wouldn't interacting with it be the cause of the wave functional collapse. I have NO IDEA what people mean when they say OBSERVE and I suspect the definition of OBSERVE has a huge bearing on understanding this.

There is a lot of other material in this writeup (thanks), but understanding the above, at least for me, will help frame this whole situation better. Could it be that you might be the one and only person who can adequately explain this?