If you data came as is (esp. your vol variables are following the ascending order, otherwise other steps will be needed), and you want to output every row for each vol, here is another alternative:
data test;
input Geocode$ Vol1 Vol2 Vol3 Vol13;
cards;
NATION 2 3 5 4
;
run;
data want;
set test;
array vol vol:;
length period $ 20;
do over vol;
period=catx('-',compress(vname(vol),,'kd'),'Month');
current_vol+vol;
output;
end;
call missing(current_vol);
drop vol:;
run;
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