Apple don't know what's been archived
It's telling about the disorganised state of the docs team that when you start with Apple's own *current* StoreKit docs (https://developer.apple.com/documentation/storekit) you are directed to https://developer.apple.com/documentation/storekit as Related Documentation: Receipt Validation Programming Guide.
I've been developing in the Apple world for around 30 years. I still have paper copies of Inside Macintosh to taunt me what quality docs look like (plus I do ports of old Mac code to modern Mac or Windows OS and the last time I did one, I couldn't rely even on the archives!)
With all the cash Apple have sitting around, I am utterly bamboozled as to why they don't see this as a problem needing fixing.
it's NOT a Swift vs Objective-C thing, it's an arrogant neglect syndrome.