I currently have an Intel NUC7I7BNH and I’m thinking about upgrading to an Intel NUC8I7BEH.
The thing is that the NUC 7 uses 2133MHz memory and, according to Intel specs, the NUC 8 only accepts 2400MHz memory, except when you browse through the compatibility list and see a couple of 2133MHz memories.
What’s the deal with that?
The funny thing is that some models, like the NUC7I7BNH says it supports 1866MHz and 2133MHz but the NUC8I7BEH and other NUC 8 models only mention 2400MHz memory.
You're reading too much into it. There's a maximum validated (and warranted) speed and everything less is implied if not stated as being supported.