I see what you're saying, amysrevenge. That would make sense eventually (after 1-2 decades had passed), if that person had regular contact with the Sindar and the Noldor weren't trying to keep secrets. But they simply can't mention the Helkaraxe without the burning of the ships coming up very soon, followed by the Kinslaying. It's not safe to talk about.
I think the thought (as presented in the most recent session) is that the truth comes out in waves, and each successive wave includes more and more trauma that the Noldor endured to get across the sea which only increases the Sindar appreciation for them, until finally the last wave comes in and topples it all to the ground. The Sindar have no reason to expect any duplicity or foul play at all - everything the Noldor did, as far as the story as they see it goes, makes them better.
(some of this Wave order I'm making up below might be wrong). But the point is that the time between these waves of truth gets shorter and shorter. The Sindar don't have a lot of time to stew on exactly what the crossing of the Helcaraxe means. Before they can get to the point of "these people who are really awesome and came over here to just save us: let's examine their story for contradictions in minute detail and see if what we believe about them is unaccountably wrong", the next wave hits.
Wave 1: They came across the sea in ships to battle Morgoth, and (we assume) were immediately attacked and the ships were destroyed by Orcs
Wave 2: Poor dead Finwe, slain by Morgoth! Those brave Noldor, coming all the way over here to avenge their king, the beloved friend of Thingol.
Wave 3: The Helcaraxe! OMG can you even imagine what they went through, just (we assume) to deliver us from our Enemy, and get their vengeance?
Wave 4: They BURNED the ships themselves? WTF man, I thought you were cool. Those ships were awesome. Wait, why would they even do that? Unless....
Wave 4.5: They did WHAT at Alqualonde? Those assholes.