When to worry about engine noises?

You really think that MILLIONS of small block Chevys that idled at 15 psi had zero oil pressure at the rods and rockers? They had idiot lights for oil pressure that tripped at 7-9 lbs.
I had a 305 in an '84 C-10 that went 369,000 miles on oil pressure just like this. No engine lives that long on zero oil pressure to the rods and mains.
The crank gets the oil first anyway.
I didn't think the oil light pressure was that high. All the figures I've seen said 3PSI.