Monsanto Attempts Defense That Would Negate All Glyphosate Lawsuits
modernfarmer.com
modernfarmer.com
Now, there's an argument that if they discovered something that contradicted EPA findings, that they should have reported it to the EPA and/or published their findings, although I'm not sure if that stands as a legal argument or just an ethical one.
But re: labeling: imagine we're talking prescription medication. One generic lists different side effects than another generic of the same type. Or even benefits. For selling a product that's chemically identical. It would be the stuff of dreams for homeopaths, who could list whatever benefit they wanted, as long as they could find a study to back it up.
Uniform labeling is sort of the (a) purpose of the elevated regulation of such products.
They could communicate to their customers through means other than the label, eg, through advertising buys, or informing the media.
They would stop producing the chemical until things are corrected.
Is your point really applicable? California has labeling laws which are independent of the US ones, eg, "This product contains chemicals known to the State of California to cause cancer and birth defects or other reproductive harm" due to 1986 California Proposition 65.
This suggests that there isn't uniform labeling across the US.
As for "voluntary" labeling, the rules have evolved to be weird sometimes, but usually if the EPA claims a chemical is safe, a company can't "override" that on their label. Besides industry specific regs, libel and anti-competitive laws come into play as well.
So even if the EPA let's you add a warning to the label, doesn't mean a competitor won't sue you for doing it. Another concern is tacit admission of guilt. It strengthens the claims made by users/plaintiffs from before a warning was put on the label. There's a lot of conflicting cya aspects to consider.
For a non EPA example of this, look at the battle over milk labeling re: rBST.