The purpose is as above,

data t1;
   do i=1 to 5;
      j=i;
     output;
        end;
run;

data t2;
  if _N_<=nobs-1 then set t1(firstobs=2 rename=(I=I_lead J=J_lead));
  set t1 nobs=nobs;
  if _N_>nobs-1 then call missing(I_lead,J_lead);
  run;

  proc print;run;