Hi,I think it means that the visa application is on its way from KCC (the central processing hub) to the local embassies. This only happens for a short period of time before the status changes to "Ready" once the local embassy has received/processed it.
The data on the website mentioned was taken at a point in time (last Friday). So all those "In Transit" will now be "Ready".
I believe that all the "In Transits" would have received interview times so at least progress has started for the OC area, which is a good thing for us all.
Yes, OC area numbers will be 900 for the month of March followed by 1100 for the month of April, as per visa bulletin.