I've had mixed results with calling Lexis helpline. I don't find the representatives to be that substantively helpful. But, if you want to see if a particular search will wield any results or something like that, or formulating a search, then they can do that for you. My preference is to find someone "on the ground" who can help get what I need or direct me.
I liked F-3's suggestion that you should keep track of how you have researched. Oftentimes, partner X may ask: "did you look here?" If you've been in fifty different databases or made 20 phone calls, you may not remember once you are on the spot. Keep a notepad with you various searches and how you went about it. That will make you look prepared and organized and will inspire in partner X confidence in your abilities to proceed with the assignment - even if there seems to be no answer. Sometimes there is no answer.
Case in point, as a junior lawyer, I once spent hours researching something. Couldn't find it, despite my best efforts. I finally saw a contact name and called that person. When I reached him and explained what I was looking for, he said "you won't find it because we never issued it, and here's why." Light bulb in my head goes off. Ugh, why didn't I think to call this person earlier? Part of the problem is that (at least in my law school) we were trained to seek the answers on our own - not to reach out to others lest there be an honor code violation or something. All answers supposedly could be found by doing one's one research by oneself. But in the real world, that is not how it always works. Oftentimes, the fastest answer can be found by reaching out -- to other colleagues in the office, to staff at relevant governmental organizations, to court staff, etc. Now, I always say to follow up and confirm whatever they are saying with your own research. But, it is often a great place to start -- or a good mid-way point to confirm your own research or help you understand something in your research. Law is not a solitary enterprise, it can and should be collaborative - without revealing confidences of course.
So, follow F-3's advice - by all means, talk to the library staff. Detail for partner X the steps you have taken and ask for any further suggestions. Show that you are organized and that you have taken initiative. If you are unsure if certain "reaching out" contacts are allowed - on a no names basis that is, ask the assigning attorney. "I've done a, b, and c and wanted to confirm that no further changes have taken place. Would it be ok if I called Y on a no names basis to ask?"
Hope all is going well this summer.