FOLIO's reference data, which we are not using, suggests that these should include "Uniform title" (aka 130, 240, or 730) and the options listed for the 2nd indicator of 246...
- No type specified
- Portion of title
- Parallel title
- Distinctive title
- Other title
- Cover title
- Added title page title
- Caption title
- Running title
- Spine title
...but I think that it would be good to add options that are relevant to other title fields (210, 222, 242, 243, 247, or 740
- Abbreviated title
- Abbreviated key title
- Collective uniform title
- Former title
- Key title
- Translation of title
- Uncontrolled related/analytical title