I wish to correct myself and offer an apology to Swift.
i now have a much better understanding of when one needs to purchase the Swift STC to use 94UL.
Simply put, if your engine airframe combination is authorized for 80/87 or MoGas, you can legally use 94UL without the Swift STC. However, if that is not the case, then your engine/airframe combo has to be evaluated for compatability with 94UL, and if compatible, then the Swift STC documents that compatability and then authorizes your usage of 94UL.
I might quibble with Swift's STC Pricing, from $0 on some combos to $450 on others, but the logic of getting the evaluation and assuring compatability before use seems sound.