SharePoint Lessons Learned

SharePoint site settings GUI will not let you create a column with a display name already in use (as an existing site column, even inherited from higher level site)

SharePoint site settings GUI will adjust the field's InternalName and StaticName both to make them unique among site columns.

When adding columns to a list, it is possible to get two fields with the same StaticName, but not with the same InternalName.

SharePoint seems to append a 0 at the end to make list columns InternalName unique, but a 1 at the end to make site column InternalName (& StaticName) unique

Installing a solution with a field with all 3 matching names xml-Title (DisplayName), xml-StaticName (StaticName), xml-Name (InternalName), will succeed but silently fail to install that field.

But it is possible to successfully install a solution a field with the same xml-Title (DisplayName), xml-StaticName (StaticName), as long as the xml-Name (InternalName) is unique.

Summary:

Site Column GUI: DisplayName must be unique. SharePoint will adjust StaticName & InternalName to keep them unique.

Feature installation of site column: xml-Name (InternalName) must be unique. SharePoint will allow duplicate DisplayName & StaticName.

List Column GUI: DisplayName must be unique. SharePoint will adjust StaticName & InternalName to keep them unique.

Adding site columns to list columns via GUI: DisplayName and StaticName don't have to be unique. SharePoint will make InternalName unique.