When Gubara escapes the photography exhibit, it's through an access door hidden behind a museum sign, which needs to be removed. When Weller arrives a few moments later, the sign is in place, covering the door.
When Nas protests that Elizabeth would have a paper trail of CIA sanctioned ops,it doesn't make sense. Elizabeth's description of her work is consistent with that of a NOC agent, who has minimal official cover story to back up her work, unlike Charles Kessler who has got the "vague boring job title, vague boring job description", which has the benefit of diplomatic immunity that a NOC doesn't have. As a NSA employee, Nas should be aware of the likelihood of this scenario.