Now that I have a chance to use SAS 9.4, the first issue is the compatibility issue for the data sets created from SAS 9.4.
There is no difference in SAS data sets between SAS 9.4 and its earlier versions (SAS 9.3 and SAS 9.2). however, the default for EXTEND OBS COUNTER is different.
In order for data sets created under SAS 9.4 to be read in earlier SAS versions, an option of EXTENDOBSCOUNTER=NO must be used.
See SAS communication "Extending the Observation Count for a 32-Bit SAS Data File" for details.
libname myfiles 'C:\MyFiles';
data myfiles.bigfile (extendobscounter=no);
libname new 'C:\NewFiles' extendobscounter=no;
libname old 'C:\OldFiles';
proc copy in=old out=new;
libname old "c:\xyz";
libname new "c:\abc";