13 night cruises - Number of formal nights?

On the RCI web site it says for 12 night and longer cruises there are 3 formal nights and 3 smart casual. EXCEPT... for 13 nights which is listed as 2 & 2. Note Casual nights are 9 so it does add up.

What to Pack

Is that a typo? Or is there a reason 13 night cruises are different? For that matter I can't recall seeing a 13 night itinerary very often - mostly Transatlantics or Hawaii long haul routes with lots of sea days. So wondering if that makes a difference.

We have been on 12 nites, 14 nites, and 15 nites - all have had 3 formal nights.

If it's a typo, it's been there for quite a while. The formal night list on the RCI website is the same as it was before our 13 night TA in April '09.

We had 3 formal nights by the way.