It was available with an online agent, but not with the MSC office or msc.com.
The customer agent at the German office told me on the phone she had no clue why it wasn´t availble , when it would be avialble ( she said probably June..!!) and why the online agent had it available on their website. She "was not the IT person" were her exact words. Sad and a pretty bad reply to a customer!
Anyway, the very friendly person at the online agent was able to help me with a booking and also later was actually the trigger for MSC themselves to finally make it available online at msc.com.
No further comment on this.
Now to my actual question. I was trying to get hold of a specific Cat "YC" cabin. No such luck as MSC only obviously makes specific cabins (up to 6 or 8 in total?) available, an own selection seems not possible, which I find rediculous.
Why can I not select any cabin within a specific category, why may I only select out of 6 or 8 cabins that MSC makes available at the time?