Stop. Changing. My. Posters

No, it is not the expectation, but it is a method for you to check.

Change the number in the URL in your address bar to the grandparentRatingKey from the episode XML to get the show data.

Example: Find grandparentRatingKey="262680" in the XML and change the URL to /library/metadata/262680.

Of if you use browser userscripts, you can install my script to just press CTRL+I on any page (i.e. the show page) in Plex to automatically open the XML data for that item.

https://gist.github.com/JonnyWong16/ec660094e4cd7233f1dd96b4b4d62e21/raw/aa1cb4380b865fe539855364fc8e5c9b3c49e375/openPlexMetadataXML.user.js

Tools like Tautulli can also export data from your entire library so you can check everything at once.