Officially, the extra info field (where the information that is italicized goes) is for "trim level, nickname, special body name, etc." This is straight from antp, the main administrator. In the case of Regency, that is a trim and that is why it goes in the extra info field and not as part of the model name.

However, sometimes I fail to see the need to even put words such as "convertible" in this field as that is what the Class field is for in the first place.