A few years back I had a serious problem with thistle in the garden beds, particularly among irises, and daylilies. I selectively used stinger, which is apparently the same as clopyralid on those problem areas. It was very effective and had no apparent effect on the irises or daylilies. At other times I also tried it on some broadleaf weeds among some daffodils and saw no problem with the daffodils.
I have not used it for a few years because I no longer have a major thistle problem, the material is expensive, and I try to avoid the use of pesticides, particularly persistent ones.
However, I regularly grow cleomes and cosmos from seed in the iris beds to give summer and fall bloom and there has not been any apparent residual problem with clopyralid.
Of coarse this is not a controlled test and subject to my aging memory. Since I only used Stinger infrequently and to target a particular problem, rather than broadcasting the material, and removed the targeted weeds afterwards, it could also be there was very little residue left in the soil. The article also refers to sensitive crops (tomatoes, etc) as being a problem. There is a good chance cosmos and cleomes are not sensitive enough plants.
I think the point is valid to be wary of any composted manure unless you are aware of the source, but I am not sure that if a little of these materials inadvertently enters our gardens via animal droppings or wayward compost that it will be an absolute tragedy to most of us weekend gardeners.
George McGowan