Stefan, as someone who has worked with chemicals almost all my working life I don't take everything in MSDS/COHSS data as gospel.
It is normal lab practice to treat all chemicals with respect, and a few with extreme care, in my case that was cyanides and Hydrofluoric acid.
Its up to you to read for yourself and decide how you handle chemicals. Photographers found from experience that Pyrogallol was more toxic than Hydroquinone not through a few experiments with lab rats.
What you are calling rash statements are just accumulated knowledge built up over a number of years. But you would find the same information coming from very different origins. LP Clerc's data came predominantly from Europe and French photographic companies, while Kodak's came from the US and the UK.
We don't need to read the original papers and sources because history has informed us how to safely use these chemicals in our photographic practice.