From GajanThe 90 days is measured from the date of the flight in question. So for your outbound flight seat selection will be able from 90 days before this flight is supposed to leave while seat selection for the inbound is 90 before departure of this flight.

If you go to MMB on the KLM website you can see which EC seats are available. It does not help going to the AF website as all seats there will be grey'd out (as the AF MMB does not have the option to purchase seats).

If you have a positive status change, in order to benefit from this you need to re-enter your FF number. You can phone KLM/AF Reservation and ask them to re-enter your FF number. .