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%let expectdate1=%sysfunc(putn(%eval(%sysfunc(today())-1),yymmddn8.));
You want to use the format yymmddn8. The 'n' means no separator.
Per http://support.sas.com/kb/24/610.html you can specify B for blank, C for colon, D for dash, N for no separator, P for period, or S for slash.