Contemporaine Day-date bi-retro question

Hi guys,

I hope you will pardon my ignorance but a question just popped into my head regarding the Contemporaine Day-date bi-retro (and retrograde date watches in general). 

I realize that with the Malte retrograde perpetual calendar, the number of days of each month are "programmed" into the mechanism such that the watch "distinguishes" among months with 31, 30, 29, and 28 days.  However, in non-perpetual (or non-annual) calendar watches with retrograde date displays, what happens on those months with less than 31 days?

In a 31-day month, the date needle/hand returns to "1" at about midnight of the 31st.  But what happens at midnight on say September 30?  Does the watch move back to "1" or does it still move forward to a non-existing 31st day of September, in which case we have to manually adjust the date (every other month of the year).

I think one of the highlights of the retrograde display is the way the needle/hand "swooshes" back to the initial position after the last date, and I just thought it would be a shame if we only get to see the watch doing this "on its own" for only 6 months during the year.  Am I missing something?Contemporaine Day-date bi-retro question

its a simple calendar and on dates with less than 31 days the
08/29/2007 - 10:44

date indicator will have to be advanced manually.

Too bad, but I guess its the same for other brands too (nt)
08/29/2007 - 16:19

k