Doubt it's mold.

Any other suggestions? Haven't seen big yellow blotches like this before.

Very strange. Never seen anything quite like that either. Can you get a pic closer into the yellow spots themselves? I'd tend to agree that is isn't any disease process. More likely necrotic tissue from a transient moisture or nutrient issue. If those are the only ones I'd just remove them and keep and eye on it.

Dave

Unfortunately I can't as they have been cut off and bagged. Hopefully I won't need to post a follow up....

Possibly an onset of early blight.

It almost looks like those leaves were trapped under something that completely blocked sunlight, but only in spots. Or maybe applied pressure on parts of the leaves and damaged their ability to photosynthesize in those areas? Weird.