Well, I was in too big a hurry -- I just returned from a long trip late last night and was happy to see the magnolia blooming, and then concerned today when I saw the condition of the flowers in daylight. Didn't bother to look closer because I was busy unpacking/packing for another trip. I just went out and took a closer look. Most of the damage seems to be at the tips of the flowers, and I'm thinking it's frost damage. So it might not be aging or disease after all.

Any insights still appreciated, but I'm pretty confident that our last freeze nipped the buds.

Thanks again!

Some magnolias were coming on when we had that last cold spell, got frosted. It is also true that there are pathogenic diseases that mar magnolia flowers here.