If the oil quantitry is "inadequate" the oil pressure gauge will give no warning until it gets sufficiently "inadequate" to cavitate the oil pump.
There are only two types of "adequate" for oil quantity, and the other is "inadequate", If the quantity is inadequate, the pump will not draw, and there will be no oil pressure, and continued operation will ruin the engine. If the oil quantity is adequate, the oil pump will create pressure and flow, and the indicator should indicate that. There's really not much in between these two conditions.
If there is a blocked oil gallery the oil pressure gauge won't show it because the back pressure will simply cause the relief valve toi open further and dump the oil into the scavange system. In these circumstances the engine will also be toast, but it may last a little longer than it would with a cavitating pump.
An O-200 I used to fly had had a starter clutch let go inside, and distribute pieces throughout the engine, including oil galleries. The engine was removed from service, and overhauled - I know, 'cause I test flew it upon reinstallation. I had oil quantity ('cause I checked) and oil pressure ('cause it indicated), but in flight, the oil pressure suddenly went to zero in downwind, so I returned immediately for an idle landing. After several ground runs where oil pressure was indicated, and a little head scratching, I flew it again, and it was fine. The following week, the owner returned it with intermittent zero oil pressure indication. The engine was taken apart again, and a piece of starter clutch was found to be lodged in an oil gallery, and blocking the pressure indication, the engine had been fine for oil pressure and supply, (other than a bit of metal being somewhere it should not have been!) The engine shop had to absorb the cost of a re-n-re, and second disassembly. After that it was fine.
If an oil pump has been damaged internally, this might show as reduced pressure, but for my experience of five years of tearing down Continentals, the oil pump has to be pretty bad before the oil pressure indication shows any difference, probably because the oil pressure relief valve was now closed all the time, and the pump could not even make the minimum pressure any more. My O-200 had always indicated on the low side of the green, though with suitable oil, never less than green. I had it overhauled, expecting to see a difference, it was the same. I had the accuracy of the oil pressure gauge checked, it was fine. It's run very well for more than 3000 hours I've flown it, so I'm not worried about low green oil pressure - it's in the green.