Cover:false comes up with exactly 1 book

in 691 titles
When I view the comments or cover browser
"My_Catalog" (my name for the catalog that Calibre generates) has only the default (missing cover) showing

I have half a dozen TXT files that have no cover set (default cover shows)
Windows XP 6.40 Calibre
BTW I assume "cover" is part of Comments? I am looking at the file
/opt/calibre/resources/metadata_sqlite.sql
and do not see a table or field for Cover