If the hogs have marks on their backs, it may be that someone in the area is artificially marking them. Sadly it happens around here as well and often the same hog will turn up with different markings, having presumably been re-marked or marked as well by someone else. Personally, I think it is unkind to the hogs and may even interfere with their social interactions – they rely heavily on their sense of smell and any foreign substance which has been put on them is bound to make them smell different.
Added to which, it really isn’t necessary to artificially mark hedgehogs. They can be identified by their natural markings and so much nicer to see hogs in their wild natural beauty, than as parodies of themselves covered with artificial marking.
I wrote some notes a while back with tips of characteristics to look out for when identifiying hedgehogs naturally, which you might find useful. I included them in the following post, as well as tips on how to tell male from female, which can also help with identification.
Good luck. I hope you will try natural identification. Happy hogwatching!