excel - VLOOKUP not returning right value - no error -

i have 2 worksheets inside of workbook use formulate report management.

a part of report includes override function in-case source data wrong / inaccurate, allows override data correct values.

i use vlookups check if resource name found in override tab, if is, return override value. working except 2 cells returning 0%. there no change in formula across sheet, other cells working except 1 cell , i'm totally stumped problem be.

formula used determine override value

=if($a2="","",if($b2<=c$1,0%,1)) (where c$1 date in header)

formula used in main sheet pick override

=if($a2 = "","",if(iserror(vlookup($a2,'manual override'!$a:f,6,false)),sumif('config pivots'!$d:$d,$a2,'config pivots'!bv:bv),vlookup($a2,'manual override'!$a:f,6,false)))

the issue seems in following line

vlookup($a2,'manual override'!$a:f,6,false) <-- returns 0 rather 100% 1 cell.

sample data below

                         override sheet            b              c           d          e           f name       end date     february 2015   march 2015  april 2015  may 2015    june 2015 joe        june 2015       100%           100%        100%       100%        100%                        main sheet - should            b              c               d          e           f           g name     override?       february 2015  march 2015  april 2015  may 2015    june 2015 joe         yes           100%           100%        100%       100%        100%                        main sheet - looks            b              c               d          e           f           g name     override?       february 2015  march 2015  april 2015  may 2015    june 2015 joe         yes           100%           100%        100%         100%          0% 

found answer, had duplicate entry in override sheet. formula technically operating correctly, human error