Have you used Type Catalogs? Type Catalogs are a great way to create a family that only includes a few types within the RFA (or just one), and then expand the number of types that are possible by entering values in a spreadsheet like format using a text editor.
For families that might have hundreds of types, it is a great way to keep your RFA file lightweight but allow you to load the types of the family that you really need in your project.
If you have created a Type Catalog, you may have noticed the first character of the first line is typically a comma (,).
Answer: The first character on the first line establishes the delimiter Revit will use in the rest of the type catalog.
There are a number of acceptable alternatives for the comma: ; : and | are also acceptable.
In order for Revit to properly read the information, every time you need to separate a parameter value or parameter name in a type catalog, you need to use the first character on the first line. If you don’t, Revit won’t display all the data in your catalog or you may receive an error message.
Next time you need to create a family that has lots of types. Try creating a type catalog to make loading the ones you want in a project simpler.
Comma for a Type Catalog - The Revit Clinic