a) What is the distinction between our data type TEXT and the SQL:2011 data type CLOB which we do not support (T041)?
TEXT type is classic type - you can do any available operation directly there. You don't need special conversions.
b) Is there a distinction between the two Postgres data types TEXT and "CHARACTER VARYING without specifying a length" - or are they only synonym terms without different functionalities and capabilities?
TEXT and varchar are pretty same types - you cannot to set limit over TEXT type - only this is visible difference