If I got this right, a single merge with every datasets will suffice.
You just need to work a subsetting if that will suite your needs.
For example the following:
[pre]
data OUT;
merge DS1 (in=D1) DS2 (in=D2) DS3 (in=D3);
by CID;
if (D1 and D2 and D3) then delete;
run;
[/pre]
Or..
[pre]
data OUT;
merge DS1 (in=D1) DS2 (in=D2) DS3 (in=D3);
by CID;
if not (D1 and D2 and D3);
run;
[/pre]
both will do the same, and will exclude the observations that full match on the 3 tables (3 way intersection).
Bare in mind that one requisite for the merge to work, is that only one of the tables may hold duplicate key values.
Check this info:
http://support.sas.com/documentation/cdl/en/lrcon/61722/HTML/default/a000761932.htm
Cheers from Portugal.
Daniel Santos @
www.cgd.pt