message from google scholar team:
I wanted to check in to see if you might be able to look into some publication date metatag errors for db-thueringen.de that are preventing the Scholar Indexing system from including these publications.
We are seeing widespread cases of incorrect publication dates in the citation_publication_date tags. Given that the citation_publication_date tag is consistently later than the actual publication date, it is possible that the upload/online date is being given as the publication date here. As Anurag said on the call (which is quite long ago now, I know!), it's preferable not to have any dates appear in this field if no publication date is available, rather than defaulting to the online date field.
Item URL: https://www.db-thueringen.de/receive/dbt_mods_00038125?q=
Incorrect citation_publication_date tag: <meta name="citation_publication_date" content="2019/02/05">
Actual publication date: 2018
Item URL: https://www.db-thueringen.de/receive/dbt_mods_00003504
Incorrect citation_publication_date tag: <meta name="citation_publication_date" content="2005/06/08">
Actual publication date: 1905.
I am hoping it would be possible to fix these errors. It would be great if the correct date appeared in citation_publication_date tags so that these items can be properly indexed in Scholar.
Please let me know if you have any questions or I can provide more information.