I apologize in advance if this has been discussed before but wanted to see if someone could clarify a question for me on fare class availability. I know that during the first part of a week (usually Tues) fares are normally updated in the system. Towards the end of the week, does Delta tend to "block" certain fare buckets in the hopes of getting people to buy a higher fare ticket and then "unblock" the lower class fares the following week? The reason I'm asking is that I priced a ticket earlier this week and checked again today and the fare was almost $250 higher. Thinking that maybe the fare classes sold out, I went to Expertflyer to check the availability on the flights and came up with the following:

T0 U0 L0 K0 Q0 H0 M9 B9 Y9 A9 P9 F9

Checking the DL website seems to confirm that the lowest fare available is an M fare. What doesn't seem to make sense to me is that when I check the seat map, there are almost 100 unassigned seats remaining on the aircraft. I understand that sometimes the seatmaps aren't updated in a timely manner however it seems like there is a large discrepancy with what shows as availabile in Expertflyer versus the seat map.

I'm going to check again for the same flights next week to see if any other class availability opens up but if anyone could shed some light on why there could be zero availability in the lower classes but the seat map shows a wide open flight I'd apprecate it. Thanks and safe travels!