It does sound like old blood and your body may be just clearing itself out, but I would talk to your doctor about it just be sure as soon as you can, if nothing else at least your mind will be at rest.
Spotting is quite normal for a couple of weeks maybe.. but 10 weeks? You should see your doctor about it. I was only spotting for about a week after my surgery and it was quite fresh clots. Yes tmi, but you asked!
My periods became quite irregular after my surgery, some periods were just 2 weeks of spotting, sometimes I spot between periods, so that could be part of your problem. I had my hormones and everything tested, nothing was found to be abnormal, but it is a reoccurring problem for me unfortunately.
I hope your doctor can help you, good luck.