I missed that too when I read it. It was my husband that was like "Rameriz didn't touch him." and I went and re-read. I can't find where they touched other then the fist bump.
Only explanation is the dot had been there for a while, as in pre Peace Talks. Indelible ink can last on the skin for a long time, magical indelible ink may be harder yet to remove. All that says given what Eb was so upset about at the beginning of the book that they were going to vote Harry out, says Carlos and Company had had Harry under surveillance for a long time. And if the dot was small enough, Harry wouldn't notice it or if he did, think anything of it.
What I am wondering rereading the final interaction between Justine/HWWBehind and Harry, about their efforts to distract Harry so they could break out the inmates of Demonreach, and what Carlos said to him as to how he was voted out. The point of that is to divide and conquer on the part of Nemesis, I bet at least one on the Senior Council is infested, they want Harry out of the way because he will find out. I wouldn't be shocked if it was The Merlin who is our man.. Interesting don't you think that he wasn't even mentioned or barely mentioned in both books, and those talks were supposed to be important, yet he wasn't there.