My Uncle has a shop on Hawthorn Road.
My Uncle has a shop
at 615 Hawthorn Road.

I was thinking the same thing too, but it gets confusing when everyone uses different prepositions in one sentence and deemed it as correct! I think on is for a place that is on a particular road but you're not certain where it is at exactly, and at is for a place that you already know where it is.

Is schlemiel correct?