pre-purchased

[FRITZ JUENGLING]

Here is a note from our person in charge of student 'stuff' at our high school:

All students who pre-purchased a yearbook will have theirs delivered directly to their homes from the yearbook company.   Last chance to get your yearbook inserts today after school, for those who have already purchased yearbooks.

Any comments on 'pre-purchased'?  Why not just 'purchased' ?  Of course, I understand it, but it looks and sounds very odd to me, especially since she switched to 'already purchased' late rin the message.
Fritz