The act of writing a script to validate the data says otherwise.
Also the people who use Excel as a primary tool are not the type that write unit tests in Python generally. Or would even think to do something like that. That is my point. You, as a developer, would think of something like that. It's not that you couldn't write similar tests with excel (you could, in any .NET language). But that you thought of doing so.
Ok then I think we're agreeing but using different bits of the same point. In Excel there is no culture of good data validation. My experience working as a developer in Python gave me that culture. Agreed.
In GGGP's case they almost certainly have no tests so I stand by the recommendation that they fight hard to get a validation system in place. Probably by moving to Python and/or a RDBMS.
>I think it is more because of your experience as a developer why you were able to spot and correct errors.
I don't feel like I spotted errors. I wrote a script to validate the data and the script told me if there were errors (there were).