STPP,Sodium Percarbonate
Along with all the rest of all and sundry chemicals sold by these various suppliers are merely repackaged bulk goods.
Your average consumer cannot purchase nor has the need for >50lbs sacks of stuff, nor >50gal containers of liquid supplies, so enterprising businesses have developed to buy the goods, break them down into smaller amounts, repackaged in various priviate label containers, mark it on, then sell it on.
If someone is selling "pure" sodium percarbonate, or advertising as such, then it should be just that. OTHO, if the stuff says "oxygen bleach" or "stain fighting...", I'd ask for clearer content.
As for hazmat papers, you'd be surprised at how many of these businesses try to skirt by and not ship items clearly labeled. There are/were sellers for instance on eBay selling pure hydrogen peroxide at 35% who will ship via USPS or UPS without clearly disclosing contents and filing proper forms.