"But they couldn't find the key with the legend "any"."
The "any" key? That's the space bar. Manufactures stopped putting a label on it because, as the most used key on the keyboard, the label would wear off and they'd have to replace the key. Not labeling became the standard, and now you have the keyboard you see in front of you.
I had to have used that 50 times when I worked at the help desk for the big TLA. I got to the point where I could tell if a user was going to have issues with pressing "any key" and would just tell them to hit the space bar. Or "W". Why "W"? Why, so it will Work!