aicraft deliveries

It looks like I have different type of problems about aircraft delivery.
I ordered 15 A321-100 with first deliveries on 14 September 1994 (game date now is just September 1992) and the 15th one due on 19 May 1995. This A321 orders were pre-order (hence the aircraft will only available 2 years later).
I then ordered 10 A320-200 (available as of 1992). In the add-on, I set to start delivery in 4 weeks with additional aircraft in subsequent 2 weeks. In general, I should get my A320 order starting in October 1992 (4 weeks after September 1994) onwards.
But what happened is that the A320 orders will only be delivered AFTER my last A321-100 order (i.e. 9 June 1995).
Both A320 and A321 belong to the same family: A320, but there is a mixed up between "available" aircraft delivery and "pre-order" aircraft delivery... The :available" aircraft delivery should begin as soon as the production complete; NOT waiting until the "pre-order" aircraft delivery ends...

It looks like I have different type of problems about aircraft delivery, too.
Delivery Date is 1986 1987 1988..
but not comes