Is the 721_1200 the 727-100 Exterior Model?
And is the 722_1200 the 727-200 Exterior Model?

If they are, then they won't work with the the v2.4 Base Pack.

For me, it works like this:
csp721_2400.exe = 727-100 Base Pack
csp722_2400.exe = 727-200 Expansion Model
csp723_2400.exe = 727 Freighter Expansion Model (727-100F/200F).

Notice that they are all v2.4. I'm not sure if there is a discount for them if you bought the Exterior Models, so you might be up for €9.99 each. :(