Hi everyone,
I need to calculate the CFO tenure. May I request for your guidance in its calculation? The data is as below:

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str4 CFOANN double(CO_PER_ROL YEAR) long(JOINED_CO REJOIN LEFTOFC LEFTCO RELEFT) str4 PCFO long GVKEY
"CFO"  5626 2006     . .     .     . . ""    1
"CFO" 35684 2007     . .     .     . . ""    1
"CFO" 35684 2008     . .     .     . . ""    1
"CFO" 35684 2009     . .     .     . . ""    1
"CFO" 35684 2010     . .     .     . . ""    1
"CFO" 35684 2011     . .     .     . . ""    1
"CFO" 20106 2012     . .     .     . . ""    1
"CFO" 20106 2013     . .     .     . . ""    1
"CFO" 64669 2013     . .     .     . . ""    1
"CFO" 64669 2014     . .     .     . . ""    1
"CFO" 20106 2015     . .     .     . . ""    1
"CFO"  5626 2016     . .     .     . . ""    1
"CFO" 60442 2017     . .     .     . . ""    1
"CFO" 60442 2018     . .     .     . . ""    1
"CFO" 62300 2018     . .     .     . . "CFO" 1
"CFO" 62300 2019     . .     .     . . "CFO" 1
"CFO" 28315 2007     . .     . 17280 . ""    2
"CFO" 33885 2008     . .     .     . . "CFO" 2
"CFO" 33885 2009     . .     .     . . "CFO" 2
"CFO" 33885 2010     . .     .     . . "CFO" 2
"CFO" 33288 2007     . .     .     . . "CFO" 3
"CFO" 33126 2006     . . 19701     . . ""    4
"CFO" 33126 2007     . . 19701     . . ""    4
"CFO" 33126 2008     . . 19701     . . ""    4
"CFO" 33126 2009     . . 19701     . . ""    4
"CFO" 33126 2010     . . 19701     . . ""    4
"CFO" 43629 2011     . .     .     . . ""    4
"CFO" 43629 2012     . .     .     . . ""    4
"CFO" 43629 2013     . .     .     . . ""    4
"CFO" 49254 2014     . .     .     . . "CFO" 4
"CFO" 49254 2015     . .     .     . . "CFO" 4
"CFO" 49254 2016     . .     .     . . "CFO" 4
"CFO" 49254 2017     . .     .     . . "CFO" 4
"CFO" 49254 2018     . .     .     . . "CFO" 4
"CFO" 49254 2019     . .     .     . . "CFO" 4
"CFO" 49254 2020     . .     .     . . "CFO" 4
"CFO" 47776 2007     . .     .     . . ""    5
"CFO" 47776 2008     . .     .     . . ""    5
"CFO" 47776 2009     . .     .     . . ""    5
"CFO" 47776 2010     . .     .     . . ""    5
"CFO" 47776 2011     . .     .     . . ""    5
"CFO" 47776 2012     . .     .     . . ""    5
"CFO" 47776 2013     . .     .     . . ""    5
"CFO" 47776 2014     . .     .     . . ""    5
"CFO" 47776 2015     . .     .     . . ""    5
"CFO" 47776 2016     . .     .     . . ""    5
"CFO" 47776 2017     . .     .     . . ""    5
"CFO" 27518 2006 15675 . 21868     . . ""    6
"CFO" 27518 2007 15675 . 21868     . . ""    6
"CFO" 37250 2008 17714 .     .     . . ""    6
"CFO" 37250 2009 17714 .     .     . . ""    6
"CFO" 37250 2010 17714 .     .     . . ""    6
"CFO" 37250 2011 17714 .     .     . . ""    6
"CFO" 37250 2012 17714 .     .     . . ""    6
"CFO" 37250 2013 17714 .     .     . . ""    6
"CFO" 37250 2014 17714 .     .     . . ""    6
"CFO" 37250 2015 17714 .     .     . . ""    6
"CFO" 37250 2016 17714 .     .     . . ""    6
"CFO" 37250 2017 17714 .     .     . . ""    6
"CFO" 37250 2018 17714 .     .     . . ""    6
"CFO" 37250 2019 17714 .     .     . . ""    6
"CFO" 65527 2020     . .     .     . . "CFO" 6
"CFO" 17980 2006     . . 20037     . . ""    7
"CFO" 17980 2007     . . 20037     . . ""    7
"CFO" 17980 2008     . . 20037     . . ""    7
"CFO" 17980 2009     . . 20037     . . ""    7
"CFO" 17980 2010     . . 20037     . . ""    7
"CFO" 17980 2011     . . 20037     . . ""    7
"CFO" 17980 2012     . . 20037     . . ""    7
"CFO" 17980 2013     . . 20037     . . ""    7
"CFO" 17980 2014     . . 20037     . . ""    7
"CFO" 17980 2015     . . 20037     . . ""    7
"CFO" 50433 2016     . .     .     . . "CFO" 7
"CFO" 50433 2017     . .     .     . . "CFO" 7
"CFO" 50433 2018     . .     .     . . "CFO" 7
"CFO" 50433 2019     . .     .     . . "CFO" 7
"CFO" 50433 2020     . .     .     . . "CFO" 7
"CFO" 24994 2006     . .     .     . . ""    8
"CFO" 24994 2007     . .     .     . . ""    8
"CFO" 24994 2008     . .     .     . . ""    8
"CFO" 24994 2009     . .     .     . . ""    8
"CFO" 24994 2010     . .     .     . . ""    8
"CFO" 24994 2011     . .     .     . . ""    8
"CFO" 24994 2012     . .     .     . . ""    8
"CFO" 24994 2013     . .     .     . . ""    8
"CFO" 24994 2014     . .     .     . . ""    8
"CFO" 51943 2015     . .     .     . . ""    8
"CFO" 51943 2016     . .     .     . . ""    8
"CFO" 51943 2017     . .     .     . . ""    8
"CFO" 51943 2018     . .     .     . . ""    8
"CFO" 51943 2019     . .     .     . . ""    8
"CFO" 49264 2007     . .     .     . . "CFO" 9
"CFO" 49264 2008     . .     .     . . "CFO" 9
"CFO" 49264 2009     . .     .     . . "CFO" 9
"CFO" 49264 2010     . .     .     . . "CFO" 9
"CFO" 49264 2011     . .     .     . . "CFO" 9
"CFO" 49264 2012     . .     .     . . "CFO" 9
"CFO" 49264 2013     . .     .     . . "CFO" 9
"CFO" 49264 2014     . .     .     . . "CFO" 9
"CFO" 49264 2015     . .     .     . . "CFO" 9
end
format %td JOINED_CO
format %td REJOIN
format %td LEFTOFC
format %td LEFTCO
format %td RELEFT
label values GVKEY GVKEY
label def GVKEY 1 "001004", modify
label def GVKEY 2 "001013", modify
label def GVKEY 3 "001034", modify
label def GVKEY 4 "001045", modify
label def GVKEY 5 "001072", modify
label def GVKEY 6 "001075", modify
label def GVKEY 7 "001076", modify
label def GVKEY 8 "001078", modify
label def GVKEY 9 "001094", modify