Nope! Office of national statistics published a CSV for postcode -> constituency name [ https://geoportal.statistics.gov.uk/datasets/6f2f35a9a0b94e7... ], and then the official gov.uk parliament API for a constituency name -> MP lookup [ https://members-api.parliament.uk/index.html ]. So all of the data is the officially available data. I humbly posit that this is a publicly owned bug.

I would guess you're taking the constituency name and doing something like this:

https://members-api.parliament.uk/api/Location/Constituency/...

returns three constituencies, all of which look fine to me, but the "Stafford" one is the middle, and you're using the data from the first returned constituency