ive never heard of this 10% rule either, but even if it is accepted it will be 10% of the interval, not 10% of the total mileage.
so on a 10,000 mile interval you can go over by 1,000 miles. which to me sounds better.
what happens next time.. as it appears that if you go 10% over each time you can save 1 in 10 services?
ie service at: 11k 22k 33k 44k 55k 66k 77k 88k 99k 110k.. you have then done 110k miles with only 10 services..
you could also miss out servicing altogether for some components if you go over intervals significantly as they could do a 50k service when a 40k is due which may have specific service items.
if you got serviced at 44k rather than 40k and was serviced at 30k previously this is a massive 40% increase in mileage not 10%.
We need to know what mileage /age you got the 30k done.