Small pet peeve but still something worth mentioning-no product made in 2025 or 2016 should have an "MSDS." MSDS were being phased out when I first started studying chemistry 20 years ago! I think around 2010 or so was when the MSDS more or less became a thing of the past. Anything new(or with a revised sheet) made since then should have an "SDS."
With that said, the claimed amount of SO2 in 2016 revision seems, well, really out of place. The bottle I have of the old stuff was one I bought in 2018 or so, and I'd guess the 2016 SDS would apply. The 2016 SDS tells us a specific gravity of 1.24. 20mL of syrup(roughly the amount I will often use when mixing working HC110 solutions), at 15% SO2 by weight, would contain 3.72g SO2 gas, a lot of which would probably be released when dissolving in water. That would turn into ~1.5L of gas, something you'd certainly notice bubbling out when mixing(I've never seen HC110 bubble when mix) and more importantly if your darkroom was not well ventilated that would at best smell so bad you wouldn't be able to stand being in there, or at worst would bring the concentration in the air up so high you WOULDN'T be able to smell it(our noses are funny like that) but it would be deadly pretty quickly.
More than likely, if I had to guess, a lot of SO2 gets added to syrup at some point or another and one of the other ingredients gets formed in situ. I don't see any sulfites listed in either SDS, but I'd be shocked if there's not at least some present, and SO2 can be used to prepare sulfites.
That's just my best guess, but suspect that KA SDS was not entirely accurate as to what is actually present in the final product. Remember too that SDSs are not intended for us to be able to reverse engineer a product, and in fact I've been known to preach to students I've mentored who start referencing them that, for a variety of reasons, they're actually a pretty poor source of information for a lot of chemistry uses. The SDS is intended to be a reference document for poeple all along the supply chain, for first responders who might have to deal with the substances in...less than ideal conditions, and as a quick, standardized reference for end users to know how to not hurt or kill themselves with a product.
To that end, most developers, and other photo chemicals for that matter, have the ability to release a not insigificant amount of SO2 if handled wrongly. Fixer can get pretty stinky if your stop bath is too acidic, for example(which is why for what I'm using now I spent some time buffering it). The 2016 K-A SDS may well reflect that.
