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.