The Diecarz website and possibly the app should offer a place you can go to help submit details that are missing from current entries. I occasionally come across cars without case letters or only have one of the 2 case letters. There should be an updating list on roadmap or the Die Carz site, when it fully rolls out, where users could work the list of entries that are missing some of the more important fields like case letter to submit and have the mods review for accuracy.

Sites like thetvdb offer a game like feature, https://www.thetvdb.com/points, where users are presented with a movie, show, actor and you are asked to enter the IMDB ID or a specific field that is missing along with the ability to skip. It helps them complete their database for finding possible duplicate entries while players can earn things like free subscription months etc by helping. This could even just be badges.