just FYI, you do not need the =TRUE part
=IF(ISNA(VLOOKUP(B80, Base!D:AZ,44,FALSE))=TRUE,PERSONAL.XLSB!FindName(B80,"BASE"),(VLOOKUP(B80, Base!D:AZ,44,FALSE)))
can become
=IF(ISNA(VLOOKUP(B80, Base!D:AZ,44,FALSE)),PERSONAL.XLSB!FindName(B80,"BASE"),(VLOOKUP(B80, Base!D:AZ,44,FALSE)))
as...