from what I can gather, if all preallocated seats have been reserved, then the seat map is no longer available for yu to look at.
Me and 3 others are flying on 29th April - we USED to be able to see the seat map and we did allocate seats. However, now we can't see the seat map & it also doesn't list our seat numbers anymore.
My friend is flying 2 days later and her seat map is still available and her pre requested seat is showing.
Hope that helps.