These are in the instanceTypes db table - an instanceTypeId is required in order to create an instance.
They are actually RDA Content Types and have just been loaded via API with /opt/folio/api/POST/instanceTypes.pl.
When loading titles (instances) it will be necessary to look at the 336 to determine which instanceTypeId to include in the JSON doc that will be POSTED via API. - 6/3/2020