I am in the process of performing a database migration from SharePoint 2003 to MOSS 2007. I am using the database migration method. For the most part, the content migrates well. However, there is one issue related to content types. I have summarized the issue/behavior in this document (shared on Google Docs).
In any document library in a migrated website (SPWeb) on MOSS 2007, Content Type Management is disabled (since 2003 does not feature content types). When I enable Content Type Management, the Document content type is displayed, and all columns are associated with this content type... including built-in columns such as Created By, Modified By and Checked Out To. This does not happen in a MOSS 2007 document library, i.e. all existing columns get associated with the Document content type, but not built-in columns.
Next, I set up a site content type with a set of new site columns. I added this content type to the migrated document library (mentioned above). The expected behavior is that the new content type is added to the document library's content types, and columns associated with this content type are added to the document library's column-set. While both of these happened, the abnormality was that the newly added columns (from the new content type) also were added to the Document content type.
There are no customizations to the document library, before or after the migration. So I cannot explain this behavior, and need some guidance to move forward with the migration.