Sure that it is just based on the spending pattern?
Being very curious, I phoned AMEX.
The information I got:
1. Emails regarding the "Turbo sparen" are still sent. Those who not have received it yet, might get it the next coming days.
2. The amount of money spent during the period 1 May 2009 till 31 August 2009 is taken as the limit. Above this limit clients can gain an extra mile for every euro, during the promotion period.