Oil Filter Bypass Valve Question

Hi,

I was changing the oil and filter today on my gf's 96 Nissan Sentra
with the 1.6L engine. After I had the old oil filter off, I shone a
flashlight up on the mating surface on the engine wall, and saw the
hole in the center, which lets oil into the engine from the filter, and
also 2 holes near the outer edge of the mating circle, next to each
other,. I believe one was the oil inlet hole, for letting oil into the
filter, and the other hole the "oil filter bypass valve". This "oil
filter bypass valve " hole had a rough lip protruding from its
circumfrerence. I thought perhaps something had been there which had
broken off, leaving this rough lip. Inside this hole was a very weak
valve, held in place by a spring pushing it from behind, I assume. I
was able to push the valve back in very easily with a pen. Seems like
the filter would only need to provide a very weak resistance in order
for the bypass valve to open and have the oil not go through the
filter.

Am I on target about this hole?
Is it the "oil filter bypass valve" ?
Is it supposed to be so weak?
Is it normal for the lip around it to be rough and uneven ?

Thanks

Thanks.