But macro lenses, that's another story. Their printed and spec'ed F stop is measured at infinity focus and is way off for any close focusing. Well probably not off at all based on how the max advertised F stop is calculated. But you do need more iso or more light to get the same exposure when you close focus.
Bellows effect is a well known fact, unavoidable, and widely documented. It is not cheating or "fine print" or hidden knowledge. I haven't older books available right now, but at least Ansel Adams'
Camera and Lens from 1948 has the formula to calculate the bellows effect. I assume the lens manufacturers assume that macro shooters are interested in their stuff more than the average joe, and know all this.
I'm supposing that a fixed focal length macro lens keeps its advertised focal length when close focusing, but could be wrong.
Some may, but none that use unit focusing do. All of my macro lenses shorten when focused to closer than infinity.
It might be interesting to some if manufacturers published a graph or a table that shows the true focal lengths at all focusing distances, but I don't think it would mean much to the general public, or much to anyone at all. For example, if I found out that my 400/2.8VR is only 390mm at minimum focusing distance, would I replace it with some other 400/2.8? Which one? And why?
Another issue is the strong focus breathing of some lenses, like the 70-200/2.8VR II but that problem has been fixed with the replacement FL version, which is absolutely stunning in every way. I would buy that one if I was a zoom shooter, but I prefer primes.