27596 is in multiple counties - you've got it listed only in Wake, but it's also Franklin county and IIRC Granville county too.
Is suspect 27596 is not the only ZIP in the country with this issue, and it can affect the results of this - Coventry was supposedly (as of a few days ago, anyway) not offering ACA plans in Franklin county, but was in Wake.
We currently include the plans from all counties in a particular zipcode rather than limiting to a specific county, but we should probably ask a user to specify their county if there's ambiguity. I'll get on adding this.
As for the data itself, it's current as of two weeks ago which is already slightly stale. This said, the data will only be as updated as the Healthcare.gov data from https://data.healthcare.gov/dataset/QHP-Individual-Medical-L...
EDIT: and thanks for your project - nice use of the data to help people get fast/easy access!