The cheese looks really nice and will probably taste great. Two observations:
The smooth surface indicates the cheese was pressed. Yes? Stilton is not pressed in the final stages.
Salting early stalled the acidification needed to create the ideal environment for the blue mold. While you are getting some blue, it is not what I would expect after 12 days. Since the blue is not being very aggressive, it may allow the "competition" to move in. As I said in another post, an acidic brine wash might help, but I can't say for sure from experience. If your cheese is not COVERED with blue in another couple of days, I would try the brine wash and see what happens. I would not pierce until you have better coverage. Otherwise you are just going to push contaminants into the cheese. Rubbing with salt right now might help control the other molds, but again, I have not had to do that.
After it ages for 60 days, you are welcome to send me a big chunk for sampling.