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[Game of Thrones] How did Daenerys know that Randyll Tarly was a lord?

At Blackwater Rush, Randyll and Dickon are among the few people who don’t kneel, but Daenerys calls Randyll forth and addresses him as my lord. We don’t see anyone tell her about him, and when Dickon comes up and says “you’ll have to kill me too,” she doesn’t know who he is, even though she has a little context and could deduce that is his son.
gpt
Considering that Varys was still serving her at the time, he would probably make a point of briefing her about generals serving her enemies, particularly the ones switching sides. Even as a second fiddle to the Tyrells, Tarlys are a very powerful house. Probably would't bother describing all of his children in greater detail.

Even if that wasn't the case, Tyrion would probably at some point after the battle have mentioned that they bald idiot they captured is actually Randyll Tarly, patriarch of one of the most powerful houses in the region.

But even if they both are actually terrible at their job, It doesn't change the fact that he's significantly older than the average soldier and wearing a significantly more expensive armor, so addressing him as a noble is a fair assumption.