Most everything you say is very complex, convoluted, and often involves speculation.

What we've seen: Sammael and Rahvin both have their cities covered in Wards to detect Channeling. As you so helpfully pointed out, Bel'al found out Moiraines presence, almost certainly due to Wards.

Thus it makes it unlikely Moiraine was able to find out about Sammael and Bel'al using the Power.

What remains is for her to find out with spies or by eavesdropping. Since it is unlikely she got into the Stone, it being the worlds most storied and defensible fortress, we can safely eliminate eavesdropping, in Tear at least.
In the same vein, I find it unlikely she could just wander around Sammael's palace (the Council of Nine's), for the same reason; seat of power, lots of guards, and she's unable to safely channel.

So we are left with her determining two Forsaken's identities, in a matter of hours each, using her own agents. We know she is not now, nor was ever, the Spymaster for the Blue Ajah, and so cannot know all Blue agents, only her own personal ones.

Even if she hears a description of Lord Brend or High Lord Samon, it is a stretch to think she could match the description with which Forsaken, since very little knowledge of them remains, even to Aes Sedai. Which is also why I discount your argument that it matters that Sammael, Bel'al, and Rahvin don't disguise themselves when dealing with their minions; it doesn't matter, because nobody knows what the Forsaken look like, the minions just know them as a very powerful, highly placed Darkfriend.

I stand by my original statement, that it just seems unlikely, given what we know, that even a wunderkind Aes Sedai like Moiraine could so specifically nail the identities of two Forsaken in a matter of hours.