No, means the rate after+9 changed
Well, regardless...the +9 to +12 interval should still be easier than the +12 to +15 interval.
EDIT: According to this spreadsheet and crossing that information with the information on the event page, it seems like the enchantment chance on the event page is the chance to that level and not from that level. I don't know for certain if the spreadsheet is correct but the person who made it (check other sliders) usually knows what they're talking about and it makes sense that it would be that way at least.
Galeas can you clarify this aswell?