Delivery issues

I try to time deliveries so that newly-introduced aircraft within a family arrives on the EIS date.

Let's take the 777-200LR in S1. Its EIS has been announced as November 18, 2005.

Since I already have aircraft in the 777 family on order, adding 772LR orders should keep it in line with four week interval deliveries, which means the last previous 777 order should be before/on October 14, 2005.

In past instances, no matter what I did to maintain such delivery dates, the next delivery of the aircraft in the same family would occur 8-10 weeks after the EIS date.

So I decided to try 8 weeks prior to EIS date, which would be before/on September 10, 2005. My last 777 family delivery is September 1, 2005, which means I should receive my first 772LR on the EIS date (November 18, 2005). Instead, it's four weeks AFTER the EIS date, and an odd 10.25 weeks after my last 777 delivery.