Variants on production line after launch.

[qunow]

In GW2, the F27 is currently under production and the F27 Mk.200 will enter production in 1959. Yet when I order some F27, there are some slots during 1965 that I can pick up, but those slots seems only applies to F27 Mk.100, if in order process I change them to Mk.200 then their delivery date will become 1970 but if I change them back to Mk.100 the delivery date would still be 1965.
Is it because the manufacturer still cannot maturely put all its capacity into manufacturing new variant 7 years after the initial introduction, or is there any restrictions in place? Note that after I order them as Mk.100, these can be edited into Mk.200.

[freshmore]

Probably because you already have Mk200 ordered until 1970 and the system won't allow you to order more before your existing order for Mk.200's. Because of having no Mk.100's coming after 1959 currently, that means the system will allow you to have those.