Like Nic says, it’s not the small discreet marks on the back of the neck that are a problem; indeed many rescues use them to identify their patients. It is the large 1” inch wide stripes that are increasingly being used. I am sure that you wouldn’t be best pleased if your regular visitor of three years Bluey turned up sporting a large stripe the entire length of his body, particularly if you got the chance to take a photo whilst the light nights are upon us. I think the problem is that many people are now using trail cameras and small discreet marks do not show up on them. It really is worth the extra effort trying to identify them by their own markings. We now have three visitors that I can identify just by their body shape alone. Boris is so distinctive that I managed to identify him the other night just by his silhouette!
It sounds like you are doing a great job, many of us keep records of our prickly visitors and any information gleaned from these secretive creatures can only be a good thing. Interesting about the sheep wool slug pellets and the self anointing (I know what you mean about the smell!). One of our lot was caught self anointing exiting the feeding station, but there was nothing in our garden out of the ordinary to trigger it. My theory is that they use it to cover up their own scent to prevent fellow hogs from following them when they just want a bit of peace and quiet. 🙂