I am a Delta Platinum flying AMS -> DTW at the end of May. I purchased an Economy ticket planning on the free upgrade to Comfort+. The seat map at the time of purchase showed 25/36 seats available and the system would let me purchase 9 Comfort+ tickets if I wanted to. Now that I have bought the ticket all of the empty seats have the dreaded "x" and I don't even get the option to request an upgrade.

Similarly, almost all of Premium Select was available, but now all "x" with no opportunity to buy my way up.

Does this ever change as we get closer to departure? Do I need to check this every day? What a pain.