You can convert between a two-digit date (d1) with the pattern YYMMDD and a four-digit date (d2) with the pattern YYYYMMDD using assignments:
d2 = DAYSTODATE(DAYS(d1,'YYMMDD',w), 'YYYYMMDD'); d1 = DAYSTODATE(DAYS(d2,'YYYYMMDD'), 'YYMMDD' ,w);