Ok, I understand now.
New profiles contain just the headers in the text section.
Profiles created by import of gedcom files, as in my case, have the biography section filled in with auto generated text using the current values from the data section and other events in the gedcom.
The text is static. There are no variables that refer to data items.
Reference numbers are dynamically generated.
If a data item is updated, the bio text must be similarly updated