Is that expected?

Seems so. WS picks up definitions from these external packages, but not from the "SuiteScript 2.0" library, so that function is likely not documented (or not documented correctly) in that library

I’m expecting the function to still work despite it not being in the library, as it’s in the docs. Is that a fair assumption?

yeah it still works just have to ignore WS underlining things like they're wrong when they're not

The NS type defs are incomplete, so I maintain my own https://github.com/burkybang/SuiteScript-2.0-Type-Declarations

Awesome.