When compiling some of your old code, you may additionally see a message such as the following:
IBM1215I W The variable I is declared without any data attributes.
The new compiler would issue this message, for example, for this declaration:
DCL I, J FIXED BIN;
While the older compilers would produce no message for this declare, the new compiler issues the message above because this declare is not equivalent to DCL (I,J) FIXED BIN;: it's actually equivalent to DCL I; DCL J FIXED BIN;.