I have seen “Not Offered” before when married segment logic was an issue. I was already confirmed in F and had been impacted by DL schedule changes. The first agent did not want to rebook me to my preferred routing because of the “Not Offered” message, and she said she couldn’t override married segment logic. I knew this to be 100% incorrect for the case of an already confirmed booking (new bookings such as OP’s case are sadly subject to it.) After escalating to a supervisor I got the flights I wanted.

So to the OP, keep checking, but unless the married segment issue changes, it’s doubtful to see this become bookable. DL would rather sell those F seats on other bookings.