If one uses an invalid format in %SYSFUNC, the error can go undetected:
%let date=%sysfunc(today(),xxx.);
%put &=date.;
Log:
 69         %let date=%sysfunc(today(),xxx.);
 70         %put &=date.;
 DATE=22602
The %SYSFUNC function should issue at least a NOTE to the log, like the PUT function does:
 69         data _null_;
 70         x = put(today(),xxx.);
                            ____
                            484
 NOTE 484-185: Format XXX was not found or could not be loaded.