My parents gave me copies of their wills, the original with their paperwork, I have done the same with my children. We have never used a solicitor but iiiif someone had stored their will with the solicitor you might find some sort of relevant paperwork to tell you who they are. It may be even if you can't find out that the solicitor may have registered the will on the National Will Register but not all do. Presumably if the executor exhausts all search options and cannot trace a will then intestacy rules are followed as though there wasn't a will written.
I knew what simple wishes and bequeaths were in my parents wills, no items were bequeathed specifically just monetary however dad's house had to be sold and cleared for his care home funds and in that scenario you can only make the best decision at that time and if you do not know or can't find out whether material item bequests have been set in the will, this would not be unusual for some, then I would just carry on doing what you need to do under the legality of power of attorney, in clearing a house to release funds for the donor you are working in their best interests. If Auntie doesn't get the vase that you discover subsequently is listed in the will, I think that is reasonable in the clearance and disposal of possessions that was needed. If anything of value is found in clearance and funds are needed, a case for selling such would be that the proceeds are needed for a care fund pot during the person's life not holding onto for inheritance reasons. It is possible also taking the vase example that the person forgets since writing the will a few years ago that the vase has been bequeathed and sells it or breaks it so an Executor can only do what they can do with the knowledge from the will and what they find after death. I really wouldn't worry at this stage.Others may be along with more thoughts.