Michelins by any chance ?I have had perfectly balanced Michelins before now, albeit some years ago.
Wheels don't always require a weight on the outside, so it may be on the inside.Saying that, I have balanced wheels and tyres many times, and occasionally you don't need to put weight on them.
I was once told that on new wheels and tyres, if the red spot on the tyre is lined up with the valve, there should rarely be need to add balance weights. A nice straight wheel and a quality tyre would help matters too.