Check Date: we extract two dates: 008/Date1, and the first date that appears in the 260 $c. Both are of the format YYYY (u is permitted in the 008).
By default, dates must match exactly in both records (008=008, 008=260$c, or 260$c=008). However, if the 008 Date1 contains a 'u', or the 260 $c date contains a dash, the XDATE crosscheck will not fail.