Unless, I think, your existing order is for a type not yet launched, and you order a type available now. In Jet Age I ordered a bunch of DC-10-10s after ordering DC-10-30s, but before the -30 certified, and still got the -10s before the -30s.
I think it is not the case for which he means, instead, I would like to raise an example below
here we may see the production slots for 744, and It is known that the minimum headway of each new planes is 40 days.
So I've ordered 14 of them, but however the slots wont move forward and my 7th 744 still staying at Jan 1989, so how about those empty slots at the front? Let it empty?
I am not going to blame any person for case like this because sami or other admin aims at not letting airlines growing too big, but minimum headway for 40 days is way too much for Very large planes, the minimum headway of old system which has 4 slots between each new plane will be more reasonable. In real world we wont see the production slots emptyed. Maybe I will like to ask my friend who is going to visit Tolouese asking airbus for the allocation of production slots.
Edit: The slot allocation of MD-11 is bit different(1 month headway), maybe sami is working on that?