I've encountered also an autonumber issue with the customer table in SharePoint. In the table with some missing ID numbers, I have 31 customers, and the last ID in the table is 40. I use this ID in a Serienumber table. However, when I convert the table to a local table to add some extra fields, and subsequently delete the SharePoint list and re-upload the table, SharePoint renumbers the IDs. As a result, Serienumber xxx is now linked to a different customer. So autonumbers are useless with sharepoint?

I have executed update queries to update all customer ID fields in all tables, ensuring that everything points back to the correct customer. However, it is crucial to be aware of SharePoint's renumbering behavior. As Richard has mentioned multiple times, autonumbers are for ACCESS, NOT FOR YOU. Yet, if SharePoint auto renumbers, it becomes my responsibility to address and fix the issue.