Is your feature request related to a problem? Please describe.
Yes. I have my own bibtex database which is my main / global / default database. I also frequently work with others on local databases that are in a given folder with a document we are working on. Others may add citations to the local bibtex file that are duplicates of something in my database but has a different key. This can cause problems when I am trying to figure out which of two seemingly identical (save different keys) completion candidates to use. In those cases I would prefer to just use the one that is in the local bibtex file.

Describe the solution you'd like
I think its too hard to automate the choice between two candidates but a simple option / annotation in the completions buffer would be enough. Would it be possible to show whether something is from a global file or the local file? This could simply be a ("global"/"local") indicator or simply just given the filename for where the candidate is comming from.

Describe alternatives you've considered
none. automating seems like more of a pain, indicating which file seems easiest.