Well those lettuce look pretty fine, except for top right. Check this post I put up last June 2015 where there is a photo demonstrating effects of aminopyralid.
You can see the lettuce looking stunted.
It takes around one growing season for soill organisms to break the aminopyralid down.
But I do not know the answers to most of your questions: you could contact Defra with a photo, and Dow Chemicals who make the herbicide.
However Mark from here its hard to be sure, perhaps there is another cause.
re flowers, I would google aminopyralid.
But as I say, its not a certainty, at least not until you check e.g. runner bean, potato, tomato.
