Yorkies come in all shapes and sizes.
The standard is not to exceed 7lbs but we know that's not always the case. Jackson is a sturdy 12lbs (although, his last vet visit, they said he was 16lbs? but it still just doesn't seem right to me- he hasn't outgrown anything, etc!) Anyways.... 4.1kg is about 9lbs I believe? Sounds you've got yourself a "teapot!"
Jackson was already 5lbs when I got him at 9 weeks old.