For many years I enjoyed stopping at 4-way stop signs, and their less common 3- and 5-way siblings. (In case any of you have missed it, the idea of these signs is that everybody stops at the intersection; each car enters the intersection in the order that the cars arrived.)
Now, I'm seeing “all-way” stop signs. These are clearly an improvement over the other signs because they solve a manufacturing problem: you make all your signs the same, instead of guessing how many you will need for each of 3, 4 and 5-way intersections. Guessing how much of each option to stock is a bane of marketing and manufacturing.
So why didn't the signs always say “all-way”? Perhaps it took a genius to think of this simplification, but I think that what we see here is an incremental improvement, where the two steps were required. I'm guessing that, thirty years ago, signs saying “all-way” would not have made as much sense. When you know that these signs are replacing the 4-way (etc.) signs, it's obvious what they mean.