Because printing the page that way, before the primary, covers the contingency of a runoff. If there is not runoff, no sweat. If there IS a runoff, the page can be used to make sure nobody casts an invalid vote. Obviously, that use was not maintained for three voters shown on this sheet ;-)
If there is no runoff, that column wouldn't be used. Ergo, the Democratic sign-in book would have no entries in the 6/24 column.
It looks to me like somebody is trying to pull a fast one (maybe laying the groundwork for an "investigation fundraiser" scam).