So the toxicity of glyphosate changes with time? That would be an interesting chemical property! I can see that there might be unusual presumably complex reasons as to how that might have occurred but what is your evidence?
Is like when bisphenol A (BPA)[1] was found to be toxic in many studies, and manufacturers started advertising baby bottles and other childcare items as "BPA Free", while replacing it with bisphenol F (BPF)[2], chemically very similar and probably just as toxic, but less studied. Toxicity does not necessarily change with time, but our knowledge about it does.
I suspect the intended meaning of the comment you're responding to is that it was thought to be less toxic when it was first introduced, not that the actual toxicity has changed.