All of which I am aware but which is irrelevant here as we are talking about the incidental rather than sollicited appearance of brands.

Exactly. Most authors don't rely upon solicited appearance of brands in their writings. The brands which most authors insert in their writings are incidental, and they help build the MC or other characters stature, whereby a reader can relate to such character. Anybody who wears Prada is probably wealthy. Anybody who wears a pair of inexpensive flip-flops could also be wealthy, but not always.

As many of us have exampled above, a reader connects with a character in a story, when such character is described by using some brands at the initial onset. An author who continuously uses the brands throughout the entirety of the story [beginning to end] should probably emphasize such energy upon the plot/climax, etc.