I'm not sure being able to verify that it's vaguely correct really solves the issue. Consider how many edge cases inhabit a "30 sheet, mind-numbingly complicated" Excel document. Verifying equivalence sounds nontrivial, to put it mildly.

Consider how many edge cases it misses. Equivalence probably shouldn't be the top priority here.

Equivalence here would definitely be the worst test, except for all the alternatives.

> They have an excel sheet next to it - they can test it against that.

It used to be that we'd fix the copy-paste bugs in the excel sheet when we converted it to a proper model, good to know that we'll now preserve them forever.