Except we have all these low ASCII characters specifically for this purpose that don't turn up in the data at all. But there is, of course, also an escape character specifically for escaping them if necessary.
Even if you find a character that really is never in the data - your encoded data will contain it. And it's inevitable that someone encodes the encoded data again. Like putting CSV in a CSV value.
You can't type any of those on a typewriter, or see them in old or simple simple editors, or no editor like just catting to a tty.
If you say those are contrived examples that don't matter any more then you have missed the point and will probably never acknowledge the point and there is no purpose in continuing to try to communicate.
One can only ever remember and type out just so many examples, and one can always contrive some response to any single or finite number of examples, but they are actually infinite, open-ended.
Having a least common denominator that is extremely low that works in all the infinite situations you never even thought of, vs just pretty low and pretty easy to meet in most common situations, is all the difference in the world.
