Actually, I think Numbers can do this, it does have sumproduct. But there is plenty it can't. Every time I try to use it, I find something missing.
Not quite sure about that in this case. I'm not using sumproduct here in the conventional sense. In Numbers it does have a simplified way to use the function purely for multiplying one array of numbers times another... but what I'm doing is closer to an offset-match, trying to identify unique records in specified ranges on two or more criteria.
From what I've read, Numbers' sumproduct function doesn't go this far. But yeah, there's plenty of other things I do that it definitely can't facilitate yet.