Currently there is not a clear way to report items that are missing data. Some items such as the gray GameCube Wavebird are mapped to old invalid eBay product IDs. Because of that, the last data available is from 2016. It is possible to report individual previous listings, but since it is the eBay product ID that is incorrect, there is no way to flag it for review.
Ideally there would be an option to report items that are mapped to old or invalid product IDs and suggest an updated one that could be reviewed by a moderator or voted on by the community.
Customer support service by UserEcho