After reading Green Lantern: Emerald Warriors, I came across a review for the title and a point was made that I tend to agree with.  There should be no unknown sectors of space.  As has always been described, the universe is like a pie with Oa at the center and the sectors spreading out from Oa like slices of that pie, thus there are 3600 slices or sectors of space.  There should be know unknown space surrounding Oa.  The Guardians are practically the oldest living beings in the universe.  They searched the universe in an effort to put an end to magic so that science would prevail.  They have a Corps patrolling the entire known universe.  How can there be unknown sectors?   
 
Now I'm not disagreeing with the use of the term 'unknown', but rather it preceding the term 'sector'.  The sectors have been mapped out. All sectors surround Oa, all sectors meet at Oa which is why it's said a Green Lantern is effectively patrolling his/her home sector while on Oa, and basically all sectors spread out infinitely from there.  But even for the Guardians' vast knowledge and longevity, I still don't believe they know everything about the universe, which is why I would think it would be better to say there are unknown 'regions' of sectors, the universe beyond what the Guardians have learned.   
 
There really is no need to add confusion to this part of the Green Lantern mythos.  It's pretty much as straight-forward as you can get and probably the easiest thing about the GL mythos to understand.   ;)

I agree rather dumb those so called all powerful all knowing Guardians had since the birth of existence to explore space their should be no stones left un turned 

" Sci Fi Writers Have No Sense Of Scale. Logically speaking, the absolute majority of the universe should be 'unknown regions/sectors' of space. "

Just to ask, where do they exactly mention unknown sectors? I don't recall anyone talking about them lately.