I had never heard of UPRN, it is an interesting concept.
I’d be interested to know how it is structured, ie does it include a checksum to ensure that wrongly transcribed numbers are (probably) rendered invalid?
And/or, could they contrive it such that a single digit error in any decimal column, even it it generated a valid address, would still be a property closeby? Not at all sure that is mathematically possible, but who knows, numbers are full of surprises, so it might be?