The 570-600 days message is just indicative (or in other words, bull &*%^) of the time taken by cases being approved now and not necessarily how much your cases would take.. For instance, they were saying 350-400 earlier this year.. It could be something entirely different by the time we actually receive the approvals..
I wouldn't put much thought into the accuracy of that estimate or its start date etc..
just my 2 cents worth..
-ab