I'm not sure what is happening, but I suggest you check to see whether the
number of logical and physical observations are the same.  Under some
circumstances (you didn't say how the observations were deleted) records
can be  only logically deleted.  In this case they still take space.

Data set functions can do this.  You need these functions: open, attrn,
and close.

Something like this:

data _null_;
  dsid = open("data set name");
  if dsid = 0 then do;
     put "Open failed";
     stop;
  end;
  rc = attrn(dsid, "ANOBS");
  put "Observations known is " rc;  /*if zero the engine does not know*/
  rc = attrn(dsid, "NLOBS");        /*how many observations there are*/
  put "Logical observations number is " rc;
  rc = attrn(dsid, "NOBS");
  put "Physical observations number is " rc;
  rc = close(dsid);
run;