As to uniqueness, I did some maths the last time this topic came up:
"You can just specify anything you want - to bore you with maths, there are 34^17 (assuming no letters I and O) possible combinations of numbers, which is about 100 million, million, million, million (1 followed by 26 zeroes)! That means every person on the planet could have 15,000 million million unique VIN numbers each
So not much chance of getting a duplicate "
https://www.rhocar.org/index.php?/forums/topic/49660-documentation-and-vin-plates/&do=findComment&comment=405489