Determining low temperature ratings for rubber seals

Temperature ratings are typically published for industrial seals so you know where they can and cannot be used.
Many sealing products have testing standards, allowing manufacturers to publish results for easy product comparison.
However, there is no standard that tells you how to determine minimum and maximum temperatures, so how do companies come up with their ratings? Further, if two suppliers offer the same type of material with vastly different temperature ratings, how do you know who is correct, or which number to trust?

Rubber isn’t just made of rubber
Rubber is made up of more than just the raw polymer (nitrile, neoprene, fluoroelastomer, etc.).
On its own, the raw polymer has very poor properties and is difficult to work with, so a variety of materials are added to improve performance and allow for easy processing.
This rubber compound is made of up certain ingredients and processing steps to achieve a particular outcome. So, while the rubber seal is not made of pure raw polymer, it is still called by the polymer name.
This is why there are thousands of neoprene rubber compounds. The raw...