This should be your defined name. You were using the COUNTA function where the row offset is (you don't want to offset from L6) It should be where height is. Like so
=OFFSET('Extract Codes'!$L$6,0,0,COUNTA('Extract Codes'!$L$6:$L795),1)
also you didn't have ' around your sheet name which is necessary when you have blanks in your sheet names.
Did that help?
Bookmarks