Geometry behaves in non-standard ways when viewed or selected using the 's' hot key when it is less than 1/1000th of the screen size.
i.e. If I make a 1 inch cubed arb8 and display it by itself I can view it until my screen size is 1000 inches or greater and I can select it for primitive editing using the 's' hot key at any screen size even though I might not be able to see it. If, however, I add a larger object to the display, I will not be able to select the first arb any more using the 's' hot key when my screen size is greater than 1000 inches.
This behavior can be confusing.
My humble recommendation would be that all displayed geometry always be selectable for all primitive and object edit options.