First, as we said last year, the Ops Team determines the selected holidays annually (with variations from year to year because we generally have very generous schedules at Thanksgiving and Christmas/New Year). So from year to year, you may see (for example) MLK offered one year and not the next.
Second, this year we will begin making a distinction when a holiday falls on a Friday. This is due to the fact that our employees function on 2 different work weeks (some M-F and others S-Th). From now on, for Friday holidays, we will specify the alternative date for those who don't normally work on Friday.