There are some items that are actually listed for 90 Deg, some examples are machined splice products, these can be used at 90 Deg ratings.
Roger
You would only be able to take credit for terminations being rated for 90C, if all the products in the same enclosure are rated for 90C. So if you install it in a panelboard or disconnect, that is likely rated for 75C, you'd have to use 75C sizing of the wire in the termination product. If you wanted to use the 90C rating, you'd have to put your splice in a separate enclosure.
One reason you might do this, is 75C sized wire just barely exceeds the capacity of the conduit you have. Maybe you are salvaging a mistake, maybe the scope expanded from what you planned on building when the rough-in was built. So you pull 90C sized wire the majority of the length, and then locally upsize it in separate enclosures to 75C sizing to connect to equipment. It also could be a value-engineering decision, although I'm skeptical of whether that would have an advantage.
The primary reason why there is value to the 90C rating of wire, is to use it for derate calculations (ampacity adjustment for bundling and temperature correction factors). The terminations would still have to meet the 75C rating (without correction/adjustment factors), but the derate calculations get to be done from the elevated wire temperature rating.
