Product Qualities off?

One of my Corps in Unimatrix 01: Montford Air Transport has a contract for the Books and Newspapers it needs and that is running now for at least 34 months at 25000 units about 260 Quality, that makes a total of 900000 units. At the moment if has 677415 Units in stock with a quality of 159. How is it possible the quality is still at such a low level?
When I use the 677415 as 100% reference and consider it was at the start only at Q100, which was higher, and add those 25000 as 3,7% with Q260 then even it out by dividing it for 103,7% I get an increase at the start of about 5Q each month. As that change lowers with the difference between starting Q and finished Q I still come to a change of over 3Q per month with which I should at least be at total Q of 202 and thats with Q100 starting and only taking the last Q-Change which is the lowest

Montford Air Transport produces at 123% due to your exceptional welfare index. This means it uses 123% of the normal 25k units of books and newspapers per month. So even with the contract, the corp will eventually run low on books and newspapers and place a new order at a quality determined by your trade strategies.

Based on other supplies, I would guess this is 120 qua. This means, when the order is completed, it will have 20+ months times 25k books and newspapers at 120 qua mixing with your contracted quality.

You will see this occur soon with services which I would guess is also contracted. Right now it has a stock good for 5.4 months. When this gets a bit lower, as use will exceed the stated 50k units/month, it will place a new order for services.

Note: I assume you are contracting exactly 100% of usage.

Argh...mkay, thought when I contract 100% usage on CM it means it contracts 100% usage and not 100% usage before other factors but ok, that seems to correct the maths...