AgeRetain.sas

data ds1;
length id dob age 8.;
format dob mmddyy10.;
informat dob ANYDTDTE.;
input id dob age;
cards;
1 03292007 .
2 06262006 .
3 . 15
4 . .
5 07252008 14
6 08242007 .
;
run;

data ds2;
length id dob 8.;
format dob mmddyy10.;
informat dob ANYDTDTE.;
input id dob ;
cards;
10 03082009
11 .
12 04102007
;
run;

data ds_comb;
	set ds1 (in=a) ds2;
	if a then DS=1; else DS=2;
	if not missing(dob) then age=floor(yrdif(dob, "24MAR21"d));
run;

ods listing;
proc print data=ds_comb noobs;
run;

Output.lst

id           dob    age    DS

 1    03/29/2007     13     1
 2    06/26/2006     14     1
 3             .     15     1
 4             .      .     1
 5    07/25/2008     12     1
 6    08/24/2007     13     1
10    03/08/2009     12     2
11             .     12     2
12    04/10/2007     13     2

Why does ID=11 have an age of 12 retained from the previous record?