Hey,
I'm one of the LibreOffice Calc maintainers and one of the people maintaining the calc automated tests.
As you might know there is no official OpenFormula test suite which in my opinion is one of the big issues with OpenFormula. To make matters worse many corner cases are not specified and therefore implementation defined resulting in problems around interoperability.
Another point is that adding new features requires to add them into an own namespace which is important for Excel interoperability. As more or less every implementation is implementing its own names for these non-specified functions it further causes interoperability issues.