God states He reveals these truths to men and they are the same truths that the Holy Spirit has been sent forth to reveal to men - Sin, His righteousness (who He is), and Judgment to come. Therefore these particular truths evidenced here in Romans 1:18- are spiritual truths that no man can come to unless it be given him by God to understand.
The truths which are evident to those without the gospel in Romans 1:18-32 are not salvific truths. In addition all of these people reject those truths. Read that section over again and see for yourself.
However these, as you stated, are some of the light/truths and if they are received God will give/bring more.
That is pure speculation on your part -- that's not in Holy Writ.
It is only God who knows when a man comes to this point and is why the scriptures states that God then gives them over to..[their sins]. Yet in that 'giving over' we must acknowledge that God was at work in their lives, He was revealing truth to them, and then at their rejection He leaves them be.
There are no exceptions. Everyone exposed to the truths which are evident to their senses are rejected. All have/will be given over to their base desires.