I am not sure there is anything in RAW, without clarification from the designers, about: Can a character with counterspell have any chance of knowing if a particular spell is being cast by someone else? There might be something else in the core books that does say that, but the quotes given in this thread do not prove that is the case and I have not found any passage in my PHB that indicates that since this thread opened two days ago.

Saying "Unless a spell has a perceptible effect, a creature might not know it was targeted by a spell at all." is not the same as saying "Unless a spell has a perceptible effect, a creature will not know a particular spell was being cast by the character in plain view that did cast a spell..." From the quotes given it seems like this is an area the game has purposefully given DMs leeway in handling.

The Rule of Fun could lead a particular group to prefer one manner of dealing with this over another. One group may prefer to never know what spells were cast unless they had a noticeable effect. Another group (such as mine) believes it would be unfair to say a wizard casting fireball (without attempting deception of some sort) can not be known to be casting a fireball when he is clearly seen acting and half the party actually have that spell in their list of known spells.